Golf balls having layers based on polyamide, ionomer, and fatty acid amide blends

ABSTRACT

Multi-piece golf balls having a solid core of at least one layer and cover of at least one layer are provided. At least one of the layers is formed from a thermoplastic polyamide composition, comprising a blend of polyamide, ethylene acid copolymer ionomer, fatty acid amide, and plasticizer. A polyamide having a transparent optical nature is preferably used in the composition. A fatty acid ester such as dipropylene glycol dibenzoate and propylene carbonate is preferably used as the plasticizer. The ball may contain an inner core and surrounding outer core layer. A rubber composition is preferably used to form the inner core and the polyamide-based composition is preferably used to form the outer core layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of co-assigned, U.S. patent application Ser. No. 13/407,883, filed Feb. 29, 2012, now issued as U.S. Pat. No. 8,987,360, the entire disclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention generally relates to multi-piece golf balls and more particularly to golf balls having at least one layer made of polyamide/ionomer/fatty acid amide compositions. In one embodiment, the composition further contains a plasticizer. The golf ball includes a core having at least one layer and cover having at least one layer. For example, the ball contains an inner core and surrounding outer core layer or a multi-layered core having an inner core, intermediate core layer, and outer core layer. A polyamide homopolymer, copolymer, blend or alloy having a transparent optical nature preferably is used in the composition. Preferably, an ethylene acid copolymer ionomer is used with a plasticizer.

Brief Review of the Related Art

Multi-piece, solid golf balls are used today by recreational and professional golfers. Basically, these golf balls contain an inner core protected by a cover. The core acts as the primary engine for the ball and the cover helps provide the ball with durability and wear-resistance. The core and cover may be single or multi-layered. For example, three-piece golf balls having an inner core, inner cover layer, and outer cover layer are popular. In other instances, golfers will use a four-piece ball containing a dual-core (inner core and surrounding outer-core layer) and dual-cover (inner cover layer and surrounding outer cover layer). Intermediate (casing) layer(s) may be disposed between the core and cover layers to impart various properties. Thus, five-piece and even six-piece balls can be made. Normally, the core layers are made of a natural or synthetic rubber material or highly neutralized ionomer polymers (HNPs). These ionomer resins are typically copolymers of an olefin such as ethylene; and an unsaturated carboxylic acid such as methacrylic acid, acrylic acid, or maleic acid. Metal ions such as sodium, lithium, zinc, and magnesium are used to neutralize the acid groups in the copolymer. The acid groups may be partially or fully neutralized.

Such ethylene acid copolymer ionomer resins are relatively hard materials having good durability, cut-resistance, and toughness. The ionomers may be used to make cover, intermediate, and core layers. When used as a core material, the hard ionomer resin helps impart a higher initial velocity to the golf ball. This is particularly advantageous for driver shots off the tee. The ball tends to have good flight distance. However, one disadvantageous feature of such balls is they tend to have a hard “feel.” Some players experience a harsher, less comfortable feel when their club face makes contact with these hard balls. The player senses less control and the harder ball tends to have low initial spin. It is generally more difficult to hit hard balls with the proper touch and spin. This can be particularly troublesome when making short approach shots with irons near the green.

Also, it is generally known that increasing the neutralization of ethylene-based ionomers reduces the processability of the material in molding operations. Such highly neutralized ethylene-based ionomers have a decreased melt flow index. Thus, manufacturers of golf balls have looked at making blends of ethylene-based ionomers to improve their melt-flow and molding properties. For example, Bulpett et al., US Patent Application Publication 2010/0048327 discloses a golf ball having at least one layer made from a composition comprising a highly neutralized ethylene acid copolymer and plasticizing agent selected from an inner salt, a chelate, a surfactant, a phospholipid, an ionic liquid, a long-chain organic carbonate, a main-chain heteroatom-substituted fatty acid, and mixtures thereof. In particular, the carboxy-terminus of fatty acid analogs with one to three heteroatoms in the fatty acid moiety are modified to form various amides, esters, ketones, alcohols, alcohol esters and nitrites thereof. Polar waxes such as 12-hydroxystearamide; N-(2-hydroxy ethyl) 12-hydroxystearamide; stearamide; glycerin monostearate; sorbitan; monostearate; and 12-hydroxy stearic acid along with less polar waxes such as N,N′-ethylene-bis-stearamide; hydrogenated castor oil (castor wax), oxidized synthetic waxes, and functionalized synthetic waxes also may be used.

Sullivan, U.S. Pat. No. 5,120,791 discloses a golf ball comprising core and cover, wherein the cover comprises a blend of: i) about 10 to about 90 percent by weight of a hard ethylene acid copolymer ionomer (greater than 50 Shore D hardness and flex modulus of 15,000 to 70,000 psi); and ii) i) about 10 to about 90 percent by weight of a soft ethylene acid copolymer ionomer (20 to 40 Shore D hardness and flex modulus of 2,000 to 10,000 psi). The ionomer composition may contain 0.5-1 wt. % of a bis-stearamide wax to prevent clumping and mixing during processing.

In addition, it is known to add fatty acid amides to polyurethane compositions to improve dispersability and mold processing as described in Ichikawa et al., U.S. Pat. No. 6,833,400. In the '400 patent, a dispersant selected from a fatty acid amide, montan wax, and polyethylene wax is used, wherein the ratio of polyurethane to dispersant is in the range of 100:0.2 to 100:3.0. The resulting polyurethane composition may be used to form a golf ball cover.

Although some ionomer and polyurethane compositions may be effective for making core layers and other components in a golf ball, there is still a need for new compositions that can impart high quality performance properties to the ball. Particularly, there is a continuing need for improved core constructions in golf balls. The core material should have good toughness and provide the ball with high resiliency. The core material, however, should not be excessively hard and stiff so that properties such as feel, softness, and spin control are sacrificed. The present invention provides golf balls having an optimum combination of properties.

SUMMARY OF THE INVENTION

The present invention relates to multi-piece golf balls comprising a core having an inner core and surrounding outer core layer; and a cover having at least one layer disposed about the dual core. The inner core has an outer surface and geometric center, while the outer core layer has an outer surface and inner surface. In one preferred embodiment, the inner core comprises a rubber composition and the outer core layer consists essentially of about 40 to about 98% by weight polyamide; about 1 to about 60% by weight fatty acid amide; and about 1 to about 60% by weight of an acid copolymer of ethylene and an α,β-unsaturated carboxylic acid, optionally including a softening monomer selected from the group consisting of alkyl acrylates and methacrylates; and a cation source present in an amount sufficient to neutralize from about 0 to about 100% of all acid groups present in the composition. In this version, the geometric center of the inner core and surface of the outer core layer each has a hardness, and the surface hardness of the outer core layer is preferably greater than the center hardness of the inner core. In another version, the polyamide-based composition is used to form the inner core and the rubber composition is used to form the outer core. In this version, the surface hardness of the outer core layer may be less than the center hardness of the inner core.

The rubber composition may have a flex modulus of 1,000 to 60,000 psi; and the polyamide composition may have a flex modulus of 20,000 to 150,000 psi such that the flex modulus of the rubber material is less than the flex modulus of the polyamide-based material. Preferably, the flex modulus of the polyamide composition is at least 15% greater than the flex modulus of the rubber composition. In this version, the center hardness of the inner core is about 15 Shore D or greater, and the surface hardness of the outer core layer is about 20 Shore D or greater.

Suitable polyamides that can be used to form the outer core layer include, for example, polyether-amide block copolymers; polyamide 6; polyamide 6,6; polyamide 6,10; polyamide 6,12; polyamide 11; polyamide 12; polyamide 6,9; and polyamide 4,6, and copolymers and blends thereof. Preferably, a transparent polyamide is used and more preferably, the polyamide has a transparency of at least about 85%. The transparent polyamide may have a glass transition temperature in the range of about 75° to about 160° C.

In one version, the fatty acid amide is a primary monoamide such as, for example, stearamide, oleamide, erucamide, behenamide, and palmitamide. In another version, substituted monoamides including, for example, lauryl oleamide, stearyl erucamide, hydroxy fatty acid amides, N-methylol fatty acid amides, and cocamide diethanolamide may be used. Bisamides are particularly preferred and include, for example, ethylene bis(stearamide), methylene bis(oleamide), and ethylene bis(oleamide). Mixtures of the foregoing fatty acid amides also may be used in the composition of this invention.

In a second preferred embodiment, the polyamide-based composition consists essentially of about 40 to about 97% by weight polyamide; about 1 to about 60% by weight fatty acid amide; and about 1 to about 60% by weight of an acid copolymer of ethylene and an α,β-unsaturated carboxylic acid, optionally including a softening monomer selected from the group consisting of alkyl acrylates and methacrylates; and a cation source present in an amount sufficient to neutralize from about 0 to about 100% of all acid groups present in the composition; and about 1 to about 60% by weight of a plasticizer. More preferably, the plasticizer is present in the composition in an amount of about 10 to about 30% by weight. The plasticizer may be a fatty acid ester and is preferably selected from the group consisting of alkyl oleate selected from the group consisting of methyl oleate, ethyl oleate, propyl oleate, butyl oleate, and octyl oleate, and mixtures thereof.

The polyamide-based compositions of this invention have a good combination of properties including Coefficient of Restitution (COR) and compression so they can be used to make any layer in the golf ball construction. The compositions help provide the finished ball with a relatively high resiliency at a given compression.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features that are characteristic of the present invention are set forth in the appended claims. However, the preferred embodiments of the invention, together with further objects and attendant advantages, are best understood by reference to the following detailed description in connection with the accompanying drawings in which:

FIG. 1 is a cross-sectional view of a three-piece golf ball having a dual-core comprising an inner core/outer core, and a cover layer made in accordance with this invention; and

FIG. 2 is a cross-sectional view of a four-piece golf ball having a dual-core comprising an inner core/outer core; an inner cover layer; and an outer cover layer made in accordance with the present invention; and

FIG. 3 is a graph showing the Coefficient of Restitution (COR) of sample polyamide materials plotted against the Hardness of the samples.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates generally to golf balls containing at least one component made from a thermoplastic polyamide composition. In a particularly preferred version, a rubber composition is used to form an inner core; and a polyamide composition is used to form an outer core layer. More particularly, in one version, the polyamide composition consists essentially of: i) about 40 to about 98 weight percent of polyamide; ii) about 1 to about 60 weight percent of fatty acid amide; iii) about 1 to about 60 weight percent of an acid copolymer of ethylene and an α,β-unsaturated carboxylic acid, optionally including a softening monomer selected from the group consisting of alkyl acrylates and methacrylates; and iv) a cation source present in an amount sufficient to neutralize from about 0% to about 100% of all acid groups present in the composition. In another version, the polyamide composition consists essentially of: i) about 40 to about 97 weight percent of polyamide; ii) about 1 to about 60 weight percent of fatty acid amide; iii) about 1 to about 60 weight percent of an acid copolymer of ethylene and an α,β-unsaturated carboxylic acid, optionally including a softening monomer selected from the group consisting of alkyl acrylates and methacrylates; iv) a cation source present in an amount sufficient to neutralize from about 0% to about 100% of all acid groups present in the composition; and v) about 1 to about 60 weight percent of a plasticizer.

Golf balls having various constructions may be made in accordance with this invention. For example, golf balls having three-piece, four-piece, and five-piece constructions with single or multi-layered core, intermediate, and cover portions may be made. The term, “layer” as used herein means generally any spherical portion of the golf ball. More particularly, in one version, a three-piece golf ball having a dual-core and a cover is made. The dual-core includes an inner core (center) and surrounding outer core layer. In another version, a four-piece golf ball comprising a dual-core and dual-cover comprising an inner cover and outer cover is made. In yet another construction, a four-piece or five-piece golf ball having a multi-layered core comprising an inner core (center), intermediate core layer, and outer core layer, may be made. The golf balls of this invention may further contain an intermediate layer(s). As used herein, the term, “intermediate layer” means a layer of the ball disposed between the core and cover. The intermediate layer also may be referred to as a casing or mantle layer. The diameter and thickness of the different layers along with properties such as hardness and compression may vary depending upon the construction and desired playing performance properties of the golf ball.

The polyamide-containing compositions disclosed herein may be used in one or more core, intermediate or cover layers. For instance, the polyamide-based compositions may be used to form an innermost core or center layer, intermediate core layer, and/or outermost core layer. Further the polyamide-based composition may be used to form an inner, intermediate or outermost cover layer. For example in a golf ball having a three-layered cover, the polyamide-containing composition may be used in any of the three layers, but preferably is used in the inner or intermediate cover layer, or both. The polyamide-comprising compositions are thermoplastic compositions and may be adjacent to another thermoplastic composition or may be adjacent to a thermosetting composition. For example, in a three (3) or more layered-core construction, the center may be a thermosetting rubber composition, an intermediate core layer may comprise a polyamide-based composition, and the outer core layer may be made from a thermosetting rubber composition. Alternatively, the center and intermediate core layer may comprise a thermosetting rubber and the outer core layer comprises the thermoplastic polyamide composition, and the like. In a two-piece construction comprising a core and a cover, either the core or cover or both layers may consist of the polyamide-based composition.

Thermoplastic Polyamides

Thermoplastic polyamides are used to form the compositions of this invention. The composition preferably consists essentially of polyamide, ethylene acid copolymer ionomer, plasticizer, and fatty acid amide as discussed further below. The composition may contain other ingredients that do not materially affect the basic and novel characteristics of the composition. For example, mineral fillers may be added to the composition as discussed further below.

In general, polyamides refer to high molecular weight polymers in which amide linkages (—CONH—) occur along the length of the molecular chain (Hawley's Condensed Chemical Dictionary, 13^(th) Ed.). Suitable polyamides for use in the compositions of this invention may be obtained, for example, by: (1) polycondensation of (a) a dicarboxylic acid, such as oxalic acid, adipic acid, sebacic acid, terephthalic acid, isophthalic acid or 1,4-cyclohexanedicarboxylic acid, with (b) a diamine, such as ethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, or decamethylenediamine, 1,4-cyclohexyldiamine or m-xylylenediamine; (2) a ring-opening polymerization of cyclic lactam, such as ε-caprolactam or ω-laurolactam; (3) polycondensation of an aminocarboxylic acid, such as 6-aminocaproic acid, 9-aminononanoic acid, 11-aminoundecanoic acid or 12-aminododecanoic acid; or (4) copolymerization of a cyclic lactam with a dicarboxylic acid and a diamine. Specific examples of suitable polyamides include, but are not limited to, nylon 6, nylon 6,6; nylon 6,10; nylon 11, and nylon 12. Aliphatic and aromatic polyamides and blends thereof may be prepared in accordance with this invention.

Different commercially-available nylon resins may be used in accordance with the present invention including, but not limited to, Trimid® and Polyram® nylon 6,6 and nylon 6 resins, available from Polymer Technology & Services, LLC; Technyl® nylon 6,6 and nylon 6 resins, available from Rhodia Engineering Plastics; Ultramid® and Capron® nylon 6 resins, available from BASF; Cristamid® and Rilsan® nylon resins, available from Arkema Inc; Vestamid® nylon resins, available from Evonik Industries; Zytel® and Elvamide® nylon resins, available from the DuPont Company; and Grivory® GTR 45 and Grilamid® TR-90, transparent nylon resins, available from Grilamid® EMS.

Different grades of polyamides and their respective properties, which may be used in accordance with this invention, are described in the following Tables I, II, and III.

TABLE I Polyamide Resins Grade Test TRIMID TECHNYL POLYRAM Property Method Units N-66 100L A205F PA100 Flexural D790 Kpsi 410 421 392 Modulus Tensile ISO 527 Psi 8,700 Strength, Ultimate Tensile D 638 Psi 12,000 12,300 12,300 Strength, Yield Elongation D638 % 50% 25% 4% at Break Elongation ISO 527 %  4% at Yield Izod D256 ft lb/in 0.933 2.14 1.03 impact Melting D3418 ° F. 491 505 493 point *TRIMID N-66 100L is a nylon 6,6 resin, available from Polymer Technology & Services, LLC. *TECHNYL A205F is a nylon 6,6 resin, available from Rhodia Engineering Plastics. *POLYRAM PA100 is a nylon 6,6 resin, available from Polymer Technology & Services, LLC.

TABLE II Polyamide Resins Grade Test ELVAMIDE ELVAMIDE ELVAMIDE Property Method Units 8061 8063 8066 Flexural D790 Kpsi 138 131 Modulus Tensile D 638 Psi 7,500 7,500 5,700 Strength Elongation D638 % 320 315 370 at break Izod impact D256 Melting D3418 ° F. 313 316 239 point *ELVAMIDE 8061, 8063, and 8066 are nylon multi-polymer resins, available from the DuPont Company.

TABLE III Polyamide Resins Test Property Method Units ZYTEL NC010 ZYTEL BK431 Flexural Modulus D790 Kpsi 247 300 Tensile Modulus ISO 527 Psi 305,000 312,000 Nominal Strain at D638 % 10 14 Break Izod impact D256 Melting point D3418 ° F. 581 610-625 *ZYTEL NC010 and BK431 are nylon multi-polymer resins, available from the DuPont Company.

Polyamide homopolymers and copolymers are suitable for use in this invention. In general, polyamide homopolymers are produced by two common methods. In the first method, a compound containing one organic acid-type end group and one amine end group is formed into a cyclic monomer. The polyamide is then formed from the monomer by a ring-opening polymerization. These polyamides are commonly designated as nylon 6, nylon 11, nylon 12, and the like, where the number indicates the number of carbon atoms making up the ring in the monomer. For example, nylon 6 is a homopolymer of caprolactam, that is, polycaprolactam.

The second method involves the condensation polymerization of a dibasic acid and a diamine. In general, this reaction takes place as follows:

These polyamides are commonly designated as nylon 4,6; nylon 6,6; nylon 6,9; nylon 6,10; nylon 6,12; and the like, where the first number indicates the number of carbon atoms connecting the two amine groups in the diamine and the second number indicates the number of carbon atoms connecting the two acid groups in the dibasic acid, including those in the acid groups. For example, nylon 6,6 is the reaction product of hexamethylenediamine and adipic acid.

Preferred polyamide homopolymers include nylon 4, nylon 6, nylon 7, nylon 11, nylon 12, nylon 13, nylon 4,6; nylon 6,6; nylon 6,9, nylon 6,10; nylon 6,12; nylon 12,12; nylon 13,13; and mixtures thereof. More preferred polyamide homopolymers include nylon 6, nylon 11, nylon 12, nylon 4,6; nylon 6,6; nylon 6,9; nylon 6,10; nylon 6,12; and mixtures thereof.

Compositions of nylon 6, nylon 6,6; nylon 11, and nylon 12 and copolymers and blends thereof are particularly effective in the present invention. More specifically, polyamide compositions having mechanical properties that do not significantly change after the composition has been exposed to moisture are particularly effective. These polyamide compositions can be used to form the outer core layer and protect the inner core from moisture. The outer core layer encapsulates the inner core so that fluids do not penetrate therein. Because the polyamide compositions are relatively stable, they are particularly effective for making outer core layers in accordance with this invention.

As discussed above, blends of polyamides also may be used in accordance with this invention. For example, a blend partially crystalline aliphatic polyamides and partially aromatic polyamides as disclosed in Liedloff et al., U.S. Pat. No. 7,348,046, the disclosure of which is hereby incorporated by reference, may be used. Another example of a group of suitable polyamides is thermoplastic polyamide elastomers. Thermoplastic polyamide elastomers typically are copolymers of a polyamide and polyester or polyether. For example, the thermoplastic polyamide elastomer can contain a polyamide (for example, nylon 6, nylon 6,6; nylon 11, nylon 12 and the like) as a hard segment and a polyether or polyester as a soft segment. In one specific example, the thermoplastic polyamides are amorphous copolyamides based on polyamide 12. Compositions of polyether-amide block copolymers, which are commonly known as Pebax® resins and are available from Arkema, Inc. (Columbs, France), are particularly effective.

Transparent Polyamides

Thermoplastic polyamides, preferably transparent thermoplastic polyamides, are used to form the compositions of this invention. Suitable polyamides and particularly transparent polyamides that may be used in accordance with this invention are described in co-pending, co-assigned U.S. patent application Ser. No. 14/309,066 (Publication US 2014/0302947), Ser. No. 14/330,189 (Publication US 2014/0323243), and Ser. No. 14/563,646, the disclosures of which are hereby incorporated by reference.

The term, “polymer” refers to, but is not limited to, oligomers, homopolymers, copolymers, terpolymers, and the like. The polymers may have various structures including, but not limited to, regular, irregular, alternating, periodic, random, block, graft, linear, branched, isotactic, syndiotactic, atactic, and the like. Polyamide polymers include, but are not limited to, polyamide copolymers (copolyamides) having two types of monomers, copolymers having three types of monomers, and copolymers having more than three types of monomers. Blends and alloys of polyamides also may be made in accordance with this invention as described further below.

By the term, “transparent,” as used herein, it is meant having a light transmission of 50 percent or greater per the test procedures, ASTM D1003, using an Illuminate C light source. In general, transparent polyamides are classified as having a microcrystalline structure or amorphous structure. Both microcrystalline and amorphous transparent polyamides may be used in the present invention. It should be understood that while a transparent polyamide is preferably included in the composition, the final composition may have a transparent, translucent, or opaque optical nature. That is, the final composition may contain various additives including fillers, coloring agents, dyes, pigments, and the like that effect the optical nature of the composition. By the term, “translucent,” as used herein, it is meant having a light transmission of greater than 1 percent per the test procedures, ASTM D1003, using an Illuminate C light source. Alternatively, the polyamide composition has a transparency of at least about 50%, and more preferably within a range having a lower limit of about 50%, 54%, 58% 60%, 65%, 68%, or 70% and an upper limit of about 75%, 75%, 80%, 84%, 90%, 92%, 94%, or 95% or greater as measured by ISO 13468-1,2 using a 2 mm thick sample measured at a wavelength of 560 nm.

Transparent polyamide polymers are commercially available, and these polyamides may be used in accordance with this invention. For example, copolyamides such as Platamid® 8020; semi-aromatic transparent polyamides such as Rilsan® Clear G170; transparent polyamides such as Rilsan® G120 Rnew; Rilsan®G830 Rnew and G830 L Rnew; Rilsan® G850; Rilsan® Clear G350 and G350L; Rilsan® G300 HI; and transparent polyamides that are partly based on bio-based raw materials such as Rilsan® Clear G830, all of which are available from Arkema, Inc. (King of Prussia, Pa.), may be used. Other suitable examples include Ultramid® polyamides, available from BASF; and Zytel™ and Dartek™ nylon resins, available from DuPont. EMS-Chemie AG (Domat/EMS, Switzerland) supplies different grades of transparent polyamides under the Grilamid mark, including; Grilamid® TR 30, TR55, TR90, XE 3997, XE 4028 grades, and these polyamides may be used per this invention. Grivory® G and GTR transparent polyamides also are available from EMS-Chemie AG and may be used in the compositions of this invention. Other suitable polyamides include Trogamid® and Vestamid® grades available from Evonik Industries, AG (Essen, Germany); Kopa® grades available from Kolon Plastics, Inc. (Gyeongsanglouk-do, Korea) Durethan® grades available from Lanxess AG (Cologne, Germany); Arlen® grades available from Mitsui Chemicals (Tokyo, Japan); and transparent amorphous nylons such as Ashlene® 726SB, 746, 747, 747, 851, D870 and D870L available from Ashley Polymers (Brooklyn, N.Y.). Still other suitable polyamides include Radici Radilon® CST copolyamides (Chgnolo d'Isola, Italy); Shakespeare Isocor® CN30XT and CN30BT nylon 610 resins (Shakespeare Engineered Nylons owned by Jarden Applied Materials of Columbia, S.C.), Toyobo Glamide® T-714E nylons (Osaka, Japan); TP Composites Elastoblend® PA12 CL nylons (Aston, Pa.); and Aegis® polyamide compositions, available from Honeywell Plastics (Morris Township, N.J.). Transparent polyamides including, but not limited to, polyether-amide, polyester-amide, polyether-ester-amide block copolymers, are particularly suitable for use in the invention herein, and more particularly, the transparent polyamide copolymers, Rilsan Clear G300 HI, Pebax Clear 300, and Pebax Clear 400 available from Arkema, Inc. (King of Prussia, Pa.) are particularly effective.

Examples of transparent polyamides that may be used in the present invention also are described in the patent literature. For example, transparent homopolyamides and copolyamides which are amorphous or which exhibit a slight crystallinity such as those described in Montanari et al., US Patent Application Publication US 2010/0140846; Montanari et al., U.S. Pat. No. 6,376,037; and Montanari et al., U.S. Pat. No. 8,399,557, the disclosures of which are hereby incorporated by reference. Also, amorphous transparent or translucent polyamides that may be formed from the condensation of diamines with dicarboxylic acids or lactams; and blends or alloys of two or more different polyamides, as described in Grimes et al., US Patent Application Publication US 2012/0223453, the disclosure of which is hereby incorporated by reference, may be used. Polyamide copolymers such as a copolymers containing polyether blocks and polyamide blocks as described in Chhun, US Patent Application Publication US 2013/0202831, the disclosure of which is hereby incorporated by reference, may be used. The polyamide copolymers described in the Chhun '831 Publication are resistant to a high-velocity impact of at least 76.2 m/s (250 ft/s) according to the EN 166 standard; and have a Charpy notched impact strength of at least 90 kJ/m² according to the ISO 179 leU standard; and preferably also has a chemical resistance such that it is capable of deforming, in flexion, by immersion in a solvent according to the ISO 22088-3 standard by at least 3% without breaking; that is light, having a density of less than 1.05 g/cm³ measured according to the ISO 1183 D standard; and that is flexible and has an elastic modulus of less than 1000 MPa, preferably of less than 800 MPa, measured according to the ISO 527-2:93-1BA standard.

Transparent polyamides that may be used in accordance with this invention also include those polyamides described in Bühler, U.S. Pat. No. 6,528,560; Torre et al., U.S. Pat. No. 6,831,136; Bühler, U.S. Pat. No. 6,943,231; Thullen et al., U.S. Pat. No. 8,309,643; Bühler, U.S. Pat. No. 8,507,598; and Hoffmann et al., US Patent Application Publication US 2010/0203275, the disclosures of which are hereby incorporated by reference.

Examples of solid spheres made from polyamides compositions and other polymer compositions and their respective properties, which may be used in accordance with this invention, are described in the following Tables IV and IVA. In the Examples provided in Tables IV and IVA, solid spheres (1.55 inch diameter) were formed by combining various compositions in an injection molding machine, or first in a twin screw extruder. The relative amounts of each component used are reported in weight %, based on the total weight of the composition. The spheres were conditioned for two weeks at 23° C. and 50% RH after molding before they were measured. By the term, “molded sphere”, as used herein, it is meant a solid sphere (1.55 inch diameter) formed and conditioned in the above-described manner. The COR, compression, and hardness of the spheres are reported in Tables IV and IVA. Referring to FIG. 3, a graph showing the Coefficient of Restitution (COR) of the Sphere Samples in Table IV plotted against the Hardness of these Samples is provided.

In Table IV, the following polyamides are particularly preferred because of their transparent optical nature: Grilamid TR90; Grivory GTR45; Rilsan Clear G 300HI; Pebax CLR300; and Grilamid TR XE 4113.

TABLE IV Spheres Made from Polyamide Compositions and Other Polymer Compositions. 1^(st) Ingredient % 2nd Ingredient % 3rd Ingredient % CoR @125 Atti Shore D Shore C *Grilamid TR90 50 Fusabond 50 0.663 125 59.6 87.1 N525 *Grilamid TR90 50 HPF2000 50 broke 159 71.7 99.1 *Grilamid TR90 50 Hytrel 3078 50 0.679 126 59.5 89.4 *Grilamid TR90 50 Pebax 2533 50 0.664 109 50.9 80.3 *Grivory GTR45 50 Fusabond 50 0.633 105 56.2 81.1 N525 *Grivory GTR45 90 Fusabond 10 0.784 182 81.8 100 N525 *Grivory GTR45 67 NBR 6300 33 0.664 176 74.5 99.9 *HPF 2000 90 Grivory GTR45 10 0.836  93 52.0 80.4 *HPF 2000 80 Grivory GTR45 20 0.818 107 54.7 83.7 *HPF 2000 70 Grivory GTR45 30 0.798 117 56.6 86.6 *HPF 2000 60 Grivory GTR45 40 0.773 131 59.5 90.2 HPF 2000 75 Pebax 2533 25 0.822  66 44.2 70.3 HPF 2000 50 Pebax 2533 50 0.774  41 36.7 61.4 HPF 2000 25 Pebax 2533 75 0.718  4 28.5 50.0 HPF 2000 90 Pebax X2009 10 broke broke 51.6 78.6 HPF 2000 80 Pebax X2009 20 broke 104 52.2 80.3 HPF 2000 50 Grilamid RDS 50 broke 145 67.5 95.7 4835 *Surlyn 9320 50 Grivory GTR45 40 Zinc Stearate 10 0.610 125 56.9 87.1 Pebax 2533 100 0.679  −36   25.7 44.6 *Grilamid TR90 100 0.836 179 82.7 — Grilamid RDS 100 0.810 175 80.8 100 4835 *Grivory GTR45 100 0.867 184 88.0 100 Pebax X2009 100 0.655 175 75.4 99.3 *Rilsan Clear G 100 0.760 169 72.6 99.0 300 HI HPF2000 100 0.857  85 77.6 47.5 Surlyn 9320 100 0.559  37 62.1 37.2 Fusabond N525 100 0.670  −45   41.6 26.0 Hytrel 3078 100 0.721  −10   52.3 29.9 Pebax 3533 100 0.693  14 31.6 53.9 Pebax 5533 100 0.622 123 59.7 84.4 Pebax 4033 100 0.621  79 45.5 71.3 Pebax 6333 100 0.592 148 68.1 92.6 Pebax 7233 100 0.620 172 75.2 98.9 *Pebax CLR300 100 0.618 141 59.8 88.0 Pebax RNEW 100 0.673  −24* 25.1 44.6 25R53 SP 01 Pebax 4533 SP 01 100 0.697  83* 41.5 71.6 Pebax MV1074 100 0.713  95 44.2 75.3 SA 01 Pebax MH1657 100 0.676  91 47.4 73.9 Grivory G355NZ 100 0.756 180 80.5 100 *Grilamid TR XE 100 0.788 176 80.8 100 4113 Grivory RDS 4836 100 broke 178 84.7 100 Nat. Nyconomer 973 100 broke 156 67.8 92.2 Polyamide 12 100 broke 178 76.7 100 Ultramid B-3 100 0.732 186 85.6 100 Nylon *calculated from DCM compression *Compositions containing transparent polyamides. Grilamid TR 90, RDS 4835, TR XE 4113, Grivory GTR 45, RDS 4836 Nat, and G355 NZ are all available from EMS-Chemie (Switzerland). The TR, G, and GTR grades are transparent. Pebax 2533, 3533, 3033, 4033, 5533, X2009, 6333, 7233, CLR 300, RNEW 25R53 SP01, 4533 SP01, MV1074 SA 01, and MH 1657 are all available from Arkema ( King of Prussia, PA). Surlyn 9320 is a VLMI ionomer available from DuPont (Wilmington DE). Fusabond N525 is a maleic anhydride modified polyolefin available from DuPont. Hytrel 3078 is a polyether-ester block copolymer available from DuPont. HPF 2000 is an ionomer resin available from DuPont. Ultramid B-3 is a Nylon 6 available from the BASF Corp (U.S. offices in Florham Park, NJ). Nyconomer 973 is a Nylon available from NYCOA (Manchester, NH). NBR 6300 is an acrylonitrile-butadiene rubber (30% acrylonitrile content) partitioned with calcium carbonate available from Alpha Plastic Chemicals (UK).

TABLE IVA Spheres Made from Polyamide/Plasticizer Compositions 1^(st) 2^(nd) CoR@125 Compression Shore D Shore C Ingredient % Ingredient % ft/s (DCM) Hardness Hardness Pebax 4033 90 Ethyl 10 0.637 62 35.1 62.8 Oleate Pebax 4033 90 Benzoflex 284 10 0.631 69 38.8 63.7 Pebax 4033 90 Jeffsol 10 0.653 67 41.9 65.9 Propylene Carbonate Pebax 4033 90 PolyTHF 250 10 0.633 63 37.5 61.1 Pebax 4033 100 — — 0.628 92 43.5 68.0 Benzoflex 284 is a 1,2-propanediol dibenzoate, available from Eastman Chemical Company. Jeffsol Propylene Carbonate is 4-Methyl-1,3-dioxolan-2-one, available from Huntsman Chemicals. PolyTHF 250 is a polytetramethylene ether glycol, available from BASF Chemicals.

As shown in above Tables IV and IVA, various polyamide compositions may be made in accordance with this invention. The resulting polyamide composition may be used to prepare a golf ball component (for example, core, casing, or cover layer) having several advantageous properties.

As noted above, it is significant that a blend comprising transparent polyamide and plasticizer may be prepared and the resulting composition has excellent properties, particularly suitable for making golf ball layers. For example, as shown in Table IVA, a blend of 90% Pebax 4033 polyamide and 10% Ethyl Oleate (plasticizer) may be prepared and the resulting composition (solid, transparent sphere) has a COR of 0.637, DCM Compression of 62, and Shore D surface hardness of 35.1.

Fatty Acid Amides

The composition further contains fatty acid amides, which contain a saturated or unsaturated alkyl chain derived from a fatty acid and can be generally classified as falling within one of the following three categories. The first is primary monoamides having the general chemical structure:

wherein R is a fatty alkyl or alkenyl chain of C₈-C₂₂ and R′═R″═H. Examples of primary monoamides include, but are not limited to stearamide, oleamide, erucamide, behenamide, and palmitamide

The second is substituted monoamides having the general chemical structure:

These substituted monoamides include secondary, tertiary, and alkanolamides, wherein R is a fatty alkyl or alkenyl chain of C₅-C₂₃; and R′ and R″ may be a hydrogen, fatty alkyl, alkenyl, aryl, or alkylene oxide condensation groups with at least one alkyl, alkenyl, aryl, or alkylene oxide group. Examples of substituted monoamides include, but are not limited to, lauryl oleamide, stearyl erucamide, hydroxy fatty acid amides, N-methylol fatty acid amides, and cocamide diethanolamide.

The third category is bisamides having the general chemical structure:

wherein, the R groups are fatty alkyl or alkenyl chains. R* is a methylene or ethylene group, and R′ and R″ may be hydrogen, fatty alkyl, alkylene, aryl, or alkylene oxide condensation groups. Examples of suitable bisamides include, but are not limited, to ethylene bis(stearamide) and methylene bis(oleamide). R could also be a hydroxy fatty acid in any of the above three categories.

Many polyamides are semi-crystalline thermoplastic polymers containing amorphous and crystalline regions. The amorphous regions contribute elasticity and the crystalline regions contribute strength and rigidity to the polymer. The polar amide groups in the backbone chains of the polyamide polymer are attracted to each other. These groups form strong hydrogen bonds between the chains, thus providing a crystalline network. In other instances, the polyamides have a fully amorphous or crystalline nature. It is also recognized that blends of amorphous polyamides and semi-crystalline polyamides may be prepared and used in accordance with this invention. For example, such amorphous/semi-crystalline polyamide blends, which may further contain toughening agents as disclosed in Epstein et al., U.S. Pat. No. 4,410,661, the disclosure of which is hereby incorporated by reference, may be used.

While not wishing to be bound by any theory, it is believed that adding the fatty acid amide may disrupt the polyamide chains. Particularly, the fatty acid amide may be added in a sufficient amount so that it partially reduces the crystallinity of the polyamide. Preferably, the crystallinity of the polyamide is reduced by at least 1%. That is, the first polyamide (containing polyamide only) composition has a first percentage of crystallinity and the second polyamide (containing polyamide and fatty acid salt) composition has a second percentage of crystallinity. In a preferred embodiment, the second crystallinity percent value is at least 1% less; or at least 2% less; or at least 4% less; or at least 8% less; or at least 10% less than the first crystallinity percent value. The crystallinity of the polyamide may be determined by conventional techniques such as differential scanning calorimetry which measures the amount of heat absorbed or released by the sample as the sample undergoes a physical transformation. Determining the crystallinity of polyamide 6 and polyamide 6,6 is particularly effective and such polyamides can be used in accordance with this invention. By partially reducing the crystallinity of the polyamide, it becomes softer and more rubbery. Since the polyamide is less hard and stiff, it can be used to form the outer core layer and help impart a softer compression to the core. The compression of the dual-core (inner core (center) and surrounding outer core layer) is preferably within the range of about 30 to about 110, more preferably within the range of about 50 to about 100, and even more preferably within the range of about 70 to about 90.

It is believed that the fatty acid amide should be added in a sufficient amount to the polyamide composition so that there is a substantial change in the crystallinity of the polyamide polymer. Thus, although the concentration of fatty acid salt may be as little as 1% by weight to form some polyamide compositions per this invention, it is preferred that the concentration of fatty acid salt be at least 5 wt. %, more preferably at least 8 wt. %, and even more preferably at least 11 wt. % based on total weight of the composition. More particularly, it is preferred that the fatty acid salt be present in an amount within a range having a lower limit of 5% or 8% or 11% or 15% or 18% or 20% and an upper limit of 22% or 25% or 30% or 40% or 50% or 60%. In one preferred embodiment, the concentration of fatty acid amide falls within the range of about 5% to about 25%. In the present invention, it is preferred that the fatty acid amide be present at a relatively high concentration to cause the crystallinity of the polyamide polymer to change substantially. This helps impart some advantageous properties to the composition making it particularly effective for use in a golf ball.

Partially and Highly Neutralized Polymers

Preferably, the thermoplastic polyamide-based composition also includes: a) an acid copolymer of ethylene and an α,β-unsaturated carboxylic acid, optionally including a softening monomer selected from the group consisting of alkyl acrylates and methacrylates; and b) a plasticizer. In one preferred embodiment, a cation source is present in an amount sufficient to neutralize greater than 20% of all acid groups present in the composition. Suitable ethylene acid copolymers and plasticizers that may be used in accordance with this invention are described in co-pending, co-assigned U.S. patent application Ser. No. 14/460,416 (Publication US 2015/0031475); Ser. No. 14/490,976 (Publication US 2015/0005108); and Ser. No. 14/527,857 (Publication US 2015/0051015), the disclosures of which are hereby incorporated by reference. The composition may comprise a highly-neutralized polymer (HNP); partially-neutralized acid polymer; or lowly-neutralized or non-neutralized acid polymer, and blends thereof as described further below. Suitable plasticizers that may be used to plasticize the thermoplastic compositions also are described further below.

Suitable HNP compositions, which will be plasticized per this invention, comprise an HNP and optionally melt-flow modifier(s), additive(s), and/or filler(s). For purposes of the present disclosure, “HNP” refers to an acid polymer after at least 70%, preferably at least 80%, more preferably at least 90%, more preferably at least 95%, and even more preferably 100%, of the acid groups present are neutralized. It is understood that the HNP may be a blend of two or more HNPs. Preferred acid polymers are copolymers of an α-olefin and a C₃-C₈ α,β-ethylenically unsaturated carboxylic acid, optionally including a softening monomer. The α-olefin is preferably selected from ethylene and propylene. The acid is preferably selected from (meth) acrylic acid, ethacrylic acid, maleic acid, crotonic acid, fumaric acid, and itaconic acid. (Meth) acrylic acid is particularly preferred. The optional softening monomer is preferably selected from alkyl (meth)acrylate, wherein the alkyl groups have from 1 to 8 carbon atoms. Preferred acid polymers include, but are not limited to, those wherein the α-olefin is ethylene, the acid is (meth) acrylic acid, and the optional softening monomer is selected from (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, methyl (meth)acrylate, and ethyl (meth) acrylate. Particularly preferred acid polymers include, but are not limited to, ethylene/(meth) acrylic acid/n-butyl acrylate, ethylene/(meth) acrylic acid/methyl acrylate, and ethylene/(meth) acrylic acid/ethyl acrylate.

Suitable acid polymers for forming the HNP also include acid polymers that are already partially neutralized. Examples of suitable partially neutralized acid polymers include, but are not limited to, Surlyn® ionomers, commercially available from E. I. du Pont de Nemours and Company; AClyn® ionomers, commercially available from Honeywell International Inc.; and Iotek® ionomers, commercially available from ExxonMobil Chemical Company. Also suitable are DuPont® HPF 1000 and DuPont® HPF 2000, ionomeric materials commercially available from E. I. du Pont de Nemours and Company. In some embodiments, very low modulus ionomer- (“VLMI-”) type ethylene-acid polymers are particularly suitable for forming the HNP, such as Surlyn® 6320, Surlyn® 8120, Surlyn® 8320, and Surlyn® 9320, commercially available from E. I. du Pont de Nemours and Company.

The α-olefin is typically present in the acid polymer in an amount of 15 wt % or greater, or 25 wt % or greater, or 40 wt % or greater, or 60 wt % or greater, based on the total weight of the acid polymer. The acid is typically present in the acid polymer in an amount within a range having a lower limit of 1 or 2 or 4 or 6 or 8 or 10 or 12 or 15 or 16 or 20 wt % and an upper limit of 20 or 25 or 26 or 30 or 35 or 40 wt %, based on the total weight of the acid polymer. The optional softening monomer is typically present in the acid polymer in an amount within a range having a lower limit of 0 or 1 or 3 or 5 or 11 or 15 or 20 wt % and an upper limit of 23 or 25 or 30 or 35 or 50 wt %, based on the total weight of the acid polymer.

Additional suitable acid polymers are more fully described, for example, in U.S. Pat. Nos. 5,691,418, 6,562,906, 6,653,382, 6,777,472, 6,762,246, 6,815,480, and 6,953,820 and U.S. Patent Application Publication Nos. 2005/0148725, 2005/0049367, 2005/0020741, 2004/0220343, and 2003/0130434, the entire disclosures of which are hereby incorporated herein by reference.

The HNP is formed by reacting the acid polymer with a sufficient amount of cation source, optionally in the presence of a high molecular weight organic acid or salt thereof, such that at least 70%, preferably at least 80%, more preferably at least 90%, more preferably at least 95%, and even more preferably 100%, of all acid groups present are neutralized. The resulting HNP composition is plasticized with a plasticizer. Suitable plasticizers are described further below. In a particular embodiment, the cation source is present in an amount sufficient to neutralize, theoretically, greater than 100%, or 105% or greater, or 110% or greater, or 115% or greater, or 120% or greater, or 125% or greater, or 200% or greater, or 250% or greater of all acid groups present in the composition. The acid polymer can be reacted with the optional high molecular weight organic acid or salt thereof and the cation source simultaneously, or the acid polymer can be reacted with the optional high molecular weight organic acid or salt thereof prior to the addition of the cation source.

Suitable cation sources include metal ions and compounds of alkali metals, alkaline earth metals, and transition metals; metal ions and compounds of rare earth elements; and combinations thereof. Preferred cation sources are metal ions and compounds of magnesium, sodium, potassium, cesium, calcium, barium, manganese, copper, zinc, tin, lithium, and rare earth metals. The acid polymer may be at least partially neutralized prior to contacting the acid polymer with the cation source to form the HNP. Methods of preparing ionomers, and the acid polymers on which ionomers are based, are disclosed, for example, in U.S. Pat. Nos. 3,264,272, and 4,351,931, and U.S. Patent Application Publication No. 2002/0013413.

Suitable high molecular weight organic acids, for both the metal salt and as a component of the ester plasticizer, are aliphatic organic acids, aromatic organic acids, saturated monofunctional organic acids, unsaturated monofunctional organic acids, multi-unsaturated monofunctional organic acids, and dimerized derivatives thereof. Particular examples of suitable organic acids include, but are not limited to, caproic acid, caprylic acid, capric acid, lauric acid, stearic acid, behenic acid, erucic acid, oleic acid, linoleic acid, myristic acid, benzoic acid, palmitic acid, phenylacetic acid, naphthalenoic acid, dimerized derivatives thereof, and combinations thereof. Salts of high molecular weight organic acids comprise the salts, particularly the barium, lithium, sodium, zinc, bismuth, chromium, cobalt, copper, potassium, strontium, titanium, tungsten, magnesium, and calcium salts, of aliphatic organic acids, aromatic organic acids, saturated monofunctional organic acids, unsaturated monofunctional organic acids, multi-unsaturated monofunctional organic acids, dimerized derivatives thereof, and combinations thereof. Suitable organic acids and salts thereof are more fully described, for example, in U.S. Pat. No. 6,756,436, the entire disclosure of which is hereby incorporated herein by reference. In a particular embodiment, the HNP composition comprises an organic acid salt in an amount of 20 phr or greater, or 25 phr or greater, or 30 phr or greater, or 35 phr or greater, or 40 phr or greater.

As discussed above, in one preferred embodiment, at least 70% of the acid groups in the acid copolymer are neutralized, and these materials are referred to as HNP materials herein. However, it is understood that other acid copolymer compositions may be used in accordance with the present invention. For example, acid copolymer compositions having acid groups that are neutralized from about 20% to about less than 70% may be used, and these materials may be referred to as partially-neutralized ionomers. For example, the partially-neutralized ionomers may have a neutralization level of about 30% to about 65%, and more particularly about 35% to 60%.

Preferred ionomers are salts of O/X- and O/X/Y-type acid copolymers, wherein O is an α-olefin, X is a C₃-C₈ α,β-ethylenically unsaturated carboxylic acid, and Y is a softening monomer. O is preferably selected from ethylene and propylene. X is preferably selected from methacrylic acid, acrylic acid, ethacrylic acid, crotonic acid, and itaconic acid. Methacrylic acid and acrylic acid are particularly preferred. Y is preferably selected from (meth)acrylate and alkyl (meth)acrylates wherein the alkyl groups have from 1 to 8 carbon atoms, including, but not limited to, n-butyl (meth)acrylate, isobutyl (meth)acrylate, methyl (meth)acrylate, and ethyl (meth)acrylate.

Preferred O/X and O/X/Y-type copolymers include, without limitation, ethylene acid copolymers, such as ethylene/(meth)acrylic acid, ethylene/(meth)acrylic acid/maleic anhydride, ethylene/(meth)acrylic acid/maleic acid mono-ester, ethylene/maleic acid, ethylene/maleic acid mono-ester, ethylene/(meth)acrylic acid/n-butyl (meth)acrylate, ethylene/(meth)acrylic acid/isobutyl (meth)acrylate, ethylene/(meth)acrylic acid/methyl (meth)acrylate, ethylene/(meth)acrylic acid/ethyl (meth)acrylate terpolymers, and the like. The term, “copolymer,” as used herein, includes polymers having two types of monomers, those having three types of monomers, and those having more than three types of monomers. Preferred α,β-ethylenically unsaturated mono- or dicarboxylic acids are (meth) acrylic acid, ethacrylic acid, maleic acid, crotonic acid, fumaric acid, itaconic acid. (Meth) acrylic acid is most preferred. As used herein, “(meth) acrylic acid” means methacrylic acid and/or acrylic acid. Likewise, “(meth)acrylate” means methacrylate and/or acrylate.

The O/X or O/X/Y-type copolymer is at least partially neutralized with a cation source. Suitable cation sources include, but are not limited to, metal ion sources, such as compounds of alkali metals, alkaline earth metals, transition metals, and rare earth elements; ammonium salts and monoamine salts; and combinations thereof. Preferred cation sources are compounds of magnesium, sodium, potassium, cesium, calcium, barium, manganese, copper, zinc, lead, tin, aluminum, nickel, chromium, lithium, and rare earth metals.

Also, as discussed above, it is recognized that the cation source is optional, and non-neutralized or lowly-neutralized compositions may be used. For example, acid copolymers having 0% to less than 20% neutralization levels may be used. Acid copolymer compositions containing plasticizers and having zero percent of the acid groups neutralized may be used per this invention. Also, acid copolymer ionomer compositions containing plasticizers, wherein 1 to 19% of the acid groups are neutralized, may be used. Particularly, acid copolymers having about 3% to about 18% and more particularly about 6% to about 15% neutralization levels may be used in accordance with this invention.

It is also recognized that acid copolymer blends may be prepared including, but not limited to, acid copolymer compositions formed from: i) blends of two or more partially-neutralized ionomers; ii) blends of two or more highly-neutralized ionomers; iii) blends of two or more non-neutralized acid copolymers and/or lowly-neutralized ionomers; iv) blends of one or more highly-neutralized ionomers with one or more partially-neutralized ionomers, and/or lowly-neutralized ionomers, and/or non-neutralized acid copolymers; v) blends of partially-neutralized ionomers with one or more highly-neutralized ionomers, and/or lowly-neutralized ionomers, and/or non-neutralized acid copolymers.

Plasticizers

As discussed above, the polyamide-based compositions of this invention contain a plasticizer. Adding the plasticizers helps to reduce the glass transition temperature (Tg) of the composition. The glass transition in a polymer is a temperature range below which a polymer is relatively brittle and above which it is rubber-like. In addition to lowering the Tg, the plasticizer may also reduce the tan δ in the temperature range above the Tg. The Tg of a polymer is measured by a Differential Scanning calorimeter or a Dynamic Mechanical Analyzer (DMA) and the DMA is used to measure tan δ. The plasticizer may also reduce the hardness and compression of the composition when compared to its non-plasticized condition. The effects of adding a plasticizer to the ethylene acid copolymer composition on Tg, flex modulus, hardness, and other physical properties are discussed further below.

The polyamide-based compositions may contain one or more plasticizers. The plasticizers that may be used in the polyamide compositions of this invention include, for example, N-butylbenzenesulfonamide (BBSA); N-ethylbenzenesulfonamide (EBSA); N-propylbenzenesulfonamide (PBSA); N-butyl-N-dodecylbenzenesulfonamide (BDBSA); N,N-dimethylbenzenesulfonamide (DMBSA); p-methylbenzenesulfonamide; o,p-toluene sulfonamide; p-toluene sulfonamide; 2-ethylhexyl-4-hydroxybenzoate; hexadecyl-4-hydroxybenzoate; 1-butyl-4-hydroxybenzoate; dioctyl phthalate; diisodecyl phthalate; di-(2-ethylhexyl) adipate; and tri-(2-ethylhexyl) phosphate; and blends thereof.

In one preferred version, the plasticizer is selected from the group of polytetramethylene ether glycol (available from BASF under the tradename, PolyTHFT™ 250); propylene carbonate (available from Huntsman Corp., under the tradename, Jeffsol™ PC); and/or dipropyleneglycol dibenzoate (available from Eastman Chemical under the tradename, Benzoflex™ 284). Mixtures of these plasticizers also may be used.

Other suitable plasticizer compounds include benzene mono-, di-, and tricarboxylic acid esters. Phthalates such as Bis(2-ethylhexyl) phthalate (DEHP), Diisononyl phthalate (DINP), Di-n-butyl phthalate (DnBP, DBP), Butyl benzyl phthalate (BBP), Diisodecyl phthalate (DIDP), Dioctyl phthalate (DnOP), Diisooctyl phthalate (DIOP), Diethyl phthalate (DEP), Diisobutyl phthalate (DIBP), and Di-n-hexyl phthalate, and blends thereof are suitable. Iso- and terephthalates such as Dioctyl terephthalate and Dinonyl isophthalate may be used. Also appropriate are trimellitates such as Trimethyl trimellitate (TMTM), Tri-(2-ethylhexyl) trimellitate (TOTM), Tri-(n-octyl,n-decyl) trimellitate, Tri-(heptyl,nonyl) trimellitate, Tri-n-octyl trimellitate; as well as benzoates, including: 2-ethylhexyl-4-hydroxy benzoate, n-octyl benzoate, methyl benzoate, and ethyl benzoate, and blends thereof.

Also suitable are alkyl diacid esters commonly based on C4-C12 alkyl dicarboxylic acids such as adipic, sebacic, azelaic, and maleic acids such as: Bis(2-ethylhexyl)adipate (DEHA), Dimethyl adipate (DMAD), Monomethyl adipate (MMAD), Dioctyl adipate (DOA), Dibutyl sebacate (DBS), Dibutyl maleate (DBM), Diisobutyl maleate (DIBM), Dioctyl sebacate (DOS), and blends thereof. Also, esters based on glycols, polyglycols and polyhydric alcohols such as poly(ethylene glycol) mono- and di-esters, cyclohexanedimethanol esters, sorbitol derivatives; and triethylene glycol dihexanoate, diethylene glycol di-2-ethylhexanoate, tetraethylene glycol diheptanoate, and ethylene glycol dioleate, and blends thereof may be used.

Fatty acids, fatty acid salts, fatty acid amides, and fatty acid esters also may be used in the compositions of this invention. Compounds such as stearic, oleic, ricinoleic, behenic, myristic, linoleic, palmitic, and lauric acid esters, salts, and mono- and bis-amides can be used. Ethyl oleate, butyl stearate, methyl acetylricinoleate, zinc oleate, ethylene bis-oleamide, and stearyl erucamide are suitable. Suitable fatty acid salts include, for example, metal stearates, erucates, laurates, oleates, palmitates, pelargonates, and the like. For example, fatty acid salts such as zinc stearate, calcium stearate, magnesium stearate, barium stearate, and the like can be used. Fatty alcohols and acetylated fatty alcohols are also suitable, as are carbonate esters such as propylene carbonate and ethylene carbonate. Mixtures of any of the plasticizers described herein also may be used in accordance with this invention. In a particularly preferred version, the fatty acid ester is an alkyl oleate selected from the group consisting of methyl, propyl, ethyl, butyl, octyl, and decyl oleates. For example, in one version, ethyl oleate is used as the plasticizer. In another version, butyl oleate or octyl oleate is used in the composition. Suitable commercially-available fatty acids include, for example, SylFat™ FA2 Tall Fatty Acid, available from Arizona Chemical. The fatty acid composition includes 2% saturated, 50% oleic, 37% linoleic (non-conjugated), and 7% linoleic (conjugated) fatty acids; and 4% other fatty acids. This fatty acid typically has an acid value in the range of 195 to 205 mg KOH/gm.

Glycerol-based esters such as soy-bean, tung, or linseed oils or their epoxidized derivatives or blends thereof can also be used as plasticizers in the present invention, as can polymeric polyester plasticizers formed from the esterification reaction of diacids and diglycols as well as from the ring-opening polymerization reaction of caprolactones with diacids or diglycols. Citrate esters and acetylated citrate esters are also suitable. Glycerol mono-, di-, and tri-oleates may be used per this invention, and in one preferred embodiment, glycerol trioleate is used as the plasticizer.

Dicarboxylic acid molecules containing both a carboxylic acid ester and a carboxylic acid salt can perform suitably as plasticizers. The magnesium salt of mono-methyl adipate and the zinc salt of mono-octyl glutarate are two such examples for this invention. Tri- and tetra-carboxylic acid esters and salts can also be used.

Also envisioned as suitable plasticizers are organophosphate and organosulfur compounds such as tricresyl phosphate (TCP), tributyl phosphate (TBP), octyldiphenyl phosphate, alkyl sulfonic acid phenyl esters (ASE); and blends thereof; and sulfonamides such as N-ethyl toluene sulfonamide, N-(2-hydroxypropyl) benzene sulfonamide, N-(n-butyl) benzene sulfonamide. Furthermore, thioester and thioether variants of the plasticizer compounds mentioned above are suitable.

Non-ester plasticizers such as alcohols, polyhydric alcohols, glycols, polyglycols, and polyethers also are suitable materials for plasticization. Materials such as polytetramethylene ether glycol, poly(ethylene glycol), and poly(propylene glycol), oleyl alcohol, and cetyl alcohol can be used. Hydrocarbon compounds, both saturated and unsaturated, linear or cyclic can be used such as mineral oils, microcrystalline waxes, or low-molecular weight polybutadiene. Halogenated hydrocarbon compounds can also be used.

Other examples of plasticizers that may be used in the polyamide-based composition of this invention include butylbenzenesulphonamide (BBSA), ethylhexyl para-hydroxybenzoate (EHPB) and decylhexyl para-hydroxybenzoate (DHPB), as disclosed in Montanari et al., U.S. Pat. No. 6,376,037, the disclosure of which is hereby incorporated by reference.

Esters and alkylamides such as phthalic acid esters including dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diheptyl phthalate, di-2-ethylhexyl phthalate, di-n-octyl phthalate, diisodecyl phthalate, ditridecyl phthalate, dicyclohexyl phthalate, butylbenzyl phthalate, diisononyl phthalate, ethylphthalylethyl glycolate, butylphthalylbutyl glycolate, diundecyl phthalate, di-2-ethylhexyl tetrahydrophthalate as disclosed in Isobe et al., U.S. Pat. No. 6,538,099, the disclosure of which is hereby incorporated by reference, also may be used.

Jacques et al., U.S. Pat. No. 7,045,185, the disclosure of which is hereby incorporated by reference, discloses sulphonamides such as N-butylbenzenesulphonamide, ethyltoluene-sulphonamide, N-cyclohexyltoluenesulphonamide, 2-ethylhexyl-para-hydroxybenzoate, 2-decylhexyl-para-hydroxybenzoate, oligoethyleneoxytetrahydrofurfuryl alcohol, or oligoethyleneoxy malonate; esters of hydroxybenzoic acid; esters or ethers of tetrahydrofurfuryl alcohol, and esters of citric acid or hydroxymalonic acid; and these plasticizers also may be used.

Sulfonamides also may be used in the present invention, and these materials are described in Fish, Jr. et al., U.S. Pat. No. 7,297,737, the disclosure of which is hereby incorporated by reference. Examples of such sulfonamides include N-alkyl benzenesulfonamides and toluenesulfonamides, particularly N-butylbenzenesulfonamide, N-(2-hydroxypropyl)benzenesulfonamide, N-ethyl-o-toluenesulfonamide, N-ethyl-p-toluenesulfonamide, o-toluenesulfonamide, p-toluenesulfonamide. Such sulfonamide plasticizers also are described in Hochstetter et al., US Patent Application Publication 2010/0183837, the disclosure of which is hereby incorporated by reference.

As noted above, the fatty acid esters are particularly preferred plasticizers in the present invention. It has been found that the fatty acid esters perform well as plasticizers in the compositions of this invention. The fatty acid esters have several advantageous properties. For example, the fatty acid esters are compatible with the polyamide polymers and ethylene acid copolymers and they tend to blend uniformly and completely with them. Also, the fatty acid esters tend to improve the resiliency and/or compression of the composition as discussed further below. The polyamide/ethylene acid copolymer/plasticizer compositions may contain other ingredients that do not materially affect the basic and novel characteristics of the composition. For example, mineral fillers may be added as discussed above. In one particular version, the composition consists essentially of polyamide and ethylene acid copolymer and plasticizer, particularly a fatty acid ester. In another particular version, the composition consists essentially of polyamide, ethylene acid copolymer, cation source sufficient to neutralize at least 20% of the acid groups present in the composition, and plasticizer, particularly a fatty acid ester.

One method of preparing the fatty acid ester involves reacting the fatty acid or mixture of fatty acids with a corresponding alcohol. The alcohol can be any alcohol including, but not limited to, linear, branched, and cyclic alcohols. The fatty acid ester is commonly a methyl, ethyl, propyl, butyl, octyl, or other alkyl ester of a carboxylic acid that contains from 4 to 30 carbon atoms. In the present invention, ethyl, butyl, octyl, and decyl esters and particularly ethyl oleate, butyl oleate, and octyl oleate are preferred fatty acid esters because of their properties. The carboxylic acid may be saturated or unsaturated. Examples of suitable saturated carboxylic acids, that is, carboxylic acids in which the carbon atoms of the alkyl chain are connected by single bonds, include but are not limited to butyric acid (chain length of C₄ and molecular weight of 88.1); capric acid (C₁₀ and MW of 172.3); lauric acid (C₁₂ and MW of 200.3); myristic acid (C₁₄ and MW of 228.4); palmitic acid (C₁₆ and MW of 256.4); stearic acid (C₁₈ and MW of 284.5); and behenic acid (C₂₂ and MW of 340.6). Examples of suitable unsaturated carboxylic acids, that is, a carboxylic acid in which there is one or more double bonds between the carbon atoms in the alkyl chain, include but are not limited to oleic acid (chain length and unsaturation C18:1; and MW of 282.5); linoleic acid (C18:2 and MW of 280.5; linolenic acid (C18:3 and MW of 278.4); and erucic acid (C22:1 and MW of 338.6).

It is believed that the plasticizer should be added in a sufficient amount to the polyamide-based composition so there is a substantial change in the stiffness and/or hardness of the composition. Thus, although the concentration of plasticizer may be as little as 1% by weight to form some compositions per this invention, it is preferred that the concentration be relatively greater. For example, it is preferred that the concentration of the plasticizer be at least 3 weight percent (wt. %). More particularly, it is preferred that the plasticizer be present in an amount within a range having a lower limit of 1% or 3% or 5% or 7% or 8% or 10% or 12% or 15% or 18% and an upper limit of 20% or 22% or 25% or 30% or 35% or 40% or 42% or 50% or 55% or 60% or 66% or 71% or 75% or 80%. In one preferred embodiment, the concentration of plasticizer falls within the range of about 7% to about 75%, preferably about 9% to about 55%, and more preferably about 15% to about 50%.

It is believed that adding the plasticizer to the polyamide-based composition helps make the composition softer and more rubbery. Adding the plasticizers to the composition helps decrease the stiffness of the composition. That is, the plasticizer helps lower the flex modulus of the composition. The flex modulus refers to the ratio of stress to strain within the elastic limit (when measured in the flexural mode) and is similar to tensile modulus. This property is used to indicate the bending stiffness of a material. The flexural modulus, which is a modulus of elasticity, is determined by calculating the slope of the linear portion of the stress-strain curve during the bending test. If the slope of the stress-strain curve is relatively steep, the material has a relatively high flexural modulus meaning the material resists deformation. The material is more rigid. If the slope is relatively flat, the material has a relatively low flexural modulus meaning the material is more easily deformed. The material is more flexible. The flex modulus can be determined in accordance with ASTM D790 standard among other testing procedures. The flex moduli of the different compositions are discussed further below.

Flex Modulus and Hardness of Composition

As discussed above, in one preferred version, the thermoplastic polyamide composition is used to form an outer core and a rubber composition is used to form an inner core. In one embodiment, the polyamide composition is relatively stiff and the rubber composition is relatively flexible. That is, in one embodiment, the flex modulus and hardness of the polyamide material is greater than the flex modulus and hardness of the rubber material.

More particularly, in one embodiment, the polyamide composition has a flex modulus lower limit of 20,000 or 30,000 or 40,000 or 50,000 or 60,000 or 70,000 or 80,000 or 90,000 or 100,000; and a flex modulus upper limit of 110,000 or 120,000 or 130,000 psi or 140,000 or 160,000 or 180,000 or 200,000 or 300,000 or 400,000 or 500,000 psi or greater. In general, the properties of flex modulus and hardness are related, whereby flex modulus measures the material's resistance to bending and hardness measures the material's resistance to indentation. In general, as the flex modulus of the material increases, the hardness of the material also increases. Thus, in one embodiment, the polyamide composition is relatively hard having a hardness of 40 Shore D or greater, or 50 Shore D or greater, or 60 Shore D or greater, or within a range having a lower limit of 40 or 50 or 60 Shore D and an upper limit of 80 or 90 or 100 Shore D.

As discussed above, it is believed that adding the plasticizer to the polyamide-based composition helps make the composition softer and more rubbery (although the polyamide/ethylene acid copolymer/fatty acid amide composition is still considered relatively stiff versus the rubber composition as discussed above.) It also is believed that adding the fatty acid amide helps make the composition softer and more rubbery. Thus, in one embodiment, the first polyamide (containing polyamide only) composition has a first flex modulus value and the second polyamide (containing polyamide, ethylene acid copolymer, fatty acid amide, and plasticizer) composition has a second flex modulus value, wherein the second flex modulus value is at least 1% less; or at least 2% less; or at least 4% less; or at least 8% less; or at least 10% less than the first modulus value.

Conversely, in one preferred version, the rubber composition is relatively flexible. More particularly, in one embodiment, the rubber composition has a flex modulus lower limit of 1,000 or 5,000 or 10,000 or 15,000 or 20,000 or 25,000 or 30,000 psi and an upper limit of 40,000 or 45,000 or 50,000 or 60,000 or 70,000 or 80,000 psi. As discussed above, the hardness and flex modulus of the material are generally related and as the hardness of the material decreases, the flex modulus of the material also decreases. Thus, in one embodiment, the rubber composition has a hardness of 30 Shore D or less; or 40 Shore D or less; or 50 Shore D or less; or 60 Shore D or less. In another embodiment, the hardness of the rubber composition falls within a range having a lower limit of 15 or 30 or 40 or 50 Shore D and an upper limit of 60 or 70 or 80 or 85 Shore D.

Test methods for measuring the flex modulus and hardness of the materials are described further below. In some instances, it may be more feasible to measure the hardness of the golf ball layer (that is, “hardness on the ball”), and this test method also is described below.

By the term, “modulus” as used herein, it is meant flexural modulus which is the ratio of stress to strain within the elastic limit (when measured in the flexural mode) and is similar to tensile modulus. This property is used to indicate the bending stiffness of a material. The flexural modulus, which is a modulus of elasticity, is determined by calculating the slope of the linear portion of the stress-strain curve during the bending test. The formula used to calculate the flexural modulus from the recorded load (F) and deflection (D) is:

$E_{B} = {\frac{3}{4}\frac{{FL}^{3}}{{bd}^{\; 3}D}}$

wherein,

L=span of specimen between supports (m);

b=width (m); and

d=thickness (m)

If the slope of the stress-strain curve is relatively steep, the material has a relatively high flexural modulus meaning the material resists deformation. The material is more rigid. If the slope is relatively flat, the material has a relatively low flexural modulus meaning the material is more easily deformed. The material is more flexible. Flexural modulus can be determined in accordance with ASTM D790 standard among other testing procedures.

Additives and Fillers

A wide variety of additives and fillers may be included in the final polyamide composition. Suitable additives and mineral fillers include, for example, precipitated hydrated silica, clay, talc, asbestos, glass fibers, aramid fibers, mica, calcium metasilicate, barium sulfate, zinc sulfide, lithopone, silicates, silicon carbide, diatomaceous earth, polyvinyl chloride, carbonates such as calcium carbonate and magnesium carbonate. Suitable metal fillers include titanium, tungsten, aluminum, bismuth, nickel, molybdenum, iron, lead, copper, boron, cobalt, beryllium, zinc, and tin. Suitable metal alloys include steel, brass, bronze, boron carbide whiskers, and tungsten carbide whiskers. Suitable metal oxide fillers include zinc oxide, iron oxide, aluminum oxide, titanium dioxide, magnesium oxide, and zirconium oxide. Suitable particulate carbonaceous fillers include graphite, carbon black, cotton flock, natural bitumen, cellulose flock, and leather fiber. Micro balloon fillers such as glass and ceramic, and fly ash fillers can also be used.

Other additives and fillers include, but are not limited to, chemical blowing and foaming agents, optical brighteners, coloring agents, fluorescent agents, whitening agents, ultraviolet (UV) light absorbers, UV light stabilizers, defoaming agents, processing aids, antioxidants, stabilizers, softening agents, fragrance components, plasticizers, and impact modifiers. In a particular embodiment, the total amount of additive(s) and filler(s) present in the polyamide composition is 25 wt. % or less; or 20 wt. % or less; or 15 wt. % or less; or 12 wt. % or less, or 10 wt. % or less; or 9 wt. % or less; or 6 wt. % or less; or 5 wt. % or less; or 4 wt. % or less; or 3 wt. % or less, based on the total weight of the polyamide composition. More particularly, the polyamide composition may include filler(s) selected from carbon black, nanoclays (e.g., Cloisite® and Nanofil® nanoclays, commercially available from Southern Clay Products, Inc., and Nanomax® and Nanomer® nanoclays, commercially available from Nanocor, Inc.), talc (e.g., Luzenac HAR® high aspect ratio talcs, commercially available from Luzenac America, Inc.), glass (e.g., glass flake, milled glass, and microglass), mica and mica-based pigments (e.g., Iriodin® pearl luster pigments, commercially available from The Merck Group), and combinations thereof. Organic fiber micropulp also may be added. Polyamide-clay nanocomposites such as an amorphous polyamide resin containing a clay material uniformly dispersed therein, as disclosed in Lan et al., U.S. Pat. No. 6,376,591 also may be used in the polyamide composition.

In another version, the polyamide compositions may contain carbon fibers or carbon fiber sheets comprising a weave of thin carbon fibers held together in a resin. In yet another version, the polyamide compositions may contain forged composite material composed of bundles of microscopic carbon fibers held together in a resin. These turbostratic carbon fibers are randomly dispersed in the resin. The structure of the forged composite material differs over traditional carbon fiber sheets. The forged composite material contains discontinuous fibers intertwined in the resin; while ordinary carbon fiber sheets are woven—they contain a weave of fibers. As a result, the forged composite material is very lightweight and has high mechanical strength.

In accordance with the present invention, golf balls containing dual-cores formed from the thermoplastic polyamide composition have several advantageous properties. For example, the dual-core helps provide the golf ball with good resiliency (distance) without sacrificing a nice feel to the ball. As discussed above, some polyamides may have a relatively high flex modulus and golf ball layers made from such a polyamide, by and in itself, can be overly stiff and brittle. If this layer is too stiff, the golf ball may have a hard “feel.” Now, in accordance with the present invention, it has been found that polyamide compositions consisting essentially of polyamide and fatty acid amide can be used to form a golf ball layer having an optimum combination of properties. Particularly, the polyamide composition may be used as a core material. The resulting ball has a relatively high coefficient of restitution (COR) allowing it to reach high velocity when struck by a golf club. Thus, the ball tends to travel a greater distance which is particularly important for driver shots off the tee. At the same time, the compositions are not excessively hard and they help impart a soft and comfortable feel to the ball. The player experiences a better sense of control and natural feeling when making the shot. Meanwhile, the compression of the dual-core (inner core (center) and surrounding outer core layer) is preferably within the range of about 25 to about 110, more preferably within the range of about 50 to about 100, and even more preferably within the range of about 70 to about 90.

Core Structure

As discussed above, the core preferably includes an inner core (center) made from a rubber composition and a surrounding outer core layer made from the thermoplastic polyamide composition of this invention.

Any suitable rubber composition known in the art may be used to make the inner core (center) of the ball in accordance with this invention. In general, such rubber compositions contain a base rubber, free-radical initiators, crosslinking agents, and filler. Suitable base rubbers include, for example, polybutadiene, ethylene-propylene rubber, ethylene-propylene-diene rubber, polyisoprene, styrene-butadiene rubber, polyalkenamers, butyl rubber, halobutyl rubber, or polystyrene elastomers.

Examples of commercially-available polybutadiene rubbers that can be used in accordance with this invention, include, but are not limited to, BR 01 and BR 1220, available from BST Elastomers of Bangkok, Thailand; SE BR 1220LA and SE BR1203, available from DOW Chemical Co of Midland, Mich.; BUDENE 1207, 1207s, 1208, and 1280 available from Goodyear, Inc of Akron, Ohio; BR 01, 51 and 730, available from Japan Synthetic Rubber (JSR) of Tokyo, Japan; BUNA CB 21, CB 22, CB 23, CB 24, CB 25, CB 29 MES, CB 60, CB Nd 60, CB 55 NF, CB 70 B, CB KA 8967, and CB 1221, available from Lanxess Corp. of Pittsburgh. Pa.; BR1208, available from LG Chemical of Seoul, South Korea; UBEPOL BR130B, BR150, BR150B, BR150L, BR230, BR360L, BR710, and VCR617, available from UBE Industries, Ltd. of Tokyo, Japan; EUROPRENE NEOCIS BR 60, INTENE 60 AF and P30AF, and EUROPRENE BR HV80, available from Polimeri Europa of Rome, Italy; AFDENE 50 and NEODENE BR40, BR45, BR50 and BR60, available from Karbochem (PTY) Ltd. of Bruma, South Africa; KBR 01, NdBr 40, NdBR-45, NdBr 60, KBR 710S, KBR 710H, and KBR 750, available from Kumho Petrochemical Co., Ltd. Of Seoul, South Korea; DIENE 55NF, 70AC, and 320 AC, available from Firestone Polymers of Akron, Ohio; and PBR-Nd Group II and Group III, available from Nizhnekamskneftekhim, Inc. of Nizhnekamsk, Tartarstan Republic.

The rubber compositions of this invention may be cured, either by pre-blending or post-blending, using conventional curing processes. Suitable curing processes include, for example, peroxide-curing, sulfur-curing, high-energy radiation, and combinations thereof. Preferably, the rubber composition contains a free-radical initiator selected from organic peroxides, high energy radiation sources capable of generating free-radicals, and combinations thereof. In one preferred version, the rubber composition is peroxide-cured. Suitable organic peroxides include, but are not limited to, dicumyl peroxide; n-butyl-4,4-di(t-butylperoxy) valerate; 1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane; 2,5-dimethyl-2,5-di(t-butylperoxy) hexane; di-t-butyl peroxide; di-t-amyl peroxide; t-butyl peroxide; t-butyl cumyl peroxide; 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3; di(2-t-butyl-peroxyisopropyl)benzene; dilauroyl peroxide; dibenzoyl peroxide; t-butyl hydroperoxide; and combinations thereof. In a particular embodiment, the free radical initiator is dicumyl peroxide, including, but not limited to Perkadox® BC, commercially available from Akzo Nobel.

Radical scavengers such as a halogenated organosulfur or metal salt thereof, organic disulfide, or inorganic disulfide compounds may be added to the rubber composition. These compounds also may function as “soft and fast agents.” As used herein, “soft and fast agent” means any compound or a blend thereof that is capable of making a core: 1) softer (having a lower compression) at a constant “coefficient of restitution” (COR); and/or 2) faster (having a higher COR at equal compression), when compared to a core equivalently prepared without a soft and fast agent. Preferred halogenated organosulfur compounds include, but are not limited to, pentachlorothiophenol (PCTP) and salts of PCTP such as zinc pentachlorothiophenol (ZnPCTP). Using PCTP and ZnPCTP in golf ball inner cores helps produce softer and faster inner cores. The PCTP and ZnPCTP compounds help increase the resiliency and the coefficient of restitution of the core. In a particular embodiment, the soft and fast agent is selected from ZnPCTP, PCTP, ditolyl disulfide, diphenyl disulfide, dixylyl disulfide, 2-nitroresorcinol, and combinations thereof.

The rubber compositions of the present invention also may include fillers, which are added to adjust the density and/or specific gravity of the material. Suitable fillers include, but are not limited to, polymeric or mineral fillers, metal fillers, metal alloy fillers, metal oxide fillers and carbonaceous fillers. The fillers can be in any suitable form including, but not limited to, flakes, fibers, whiskers, fibrils, plates, particles, and powders. Rubber regrind, which is ground, recycled rubber material (for example, ground to about 30 mesh particle size) obtained from discarded rubber golf ball cores, also can be used as a filler. The amount and type of fillers utilized are governed by the amount and weight of other ingredients in the golf ball, since a maximum golf ball weight of 45.93 g (1.62 ounces) has been established by the United States Golf Association (USGA).

Preferably, the base rubber material is polybutadiene rubber, and this material may be blended with other elastomers in accordance with this invention. Other elastomers include, but are not limited to, polybutadiene, polyisoprene, ethylene propylene rubber (“EPR”), styrene-butadiene rubber, styrenic block copolymer rubbers (such as “SI”, “SIS”, “SB”, “SBS”, “SIBS”, and the like, where “S” is styrene, “I” is isobutylene, and “B” is butadiene), polyalkenamers such as, for example, polyoctenamer, butyl rubber, halobutyl rubber, polystyrene elastomers, polyethylene elastomers, polyurethane elastomers, polyurea elastomers, metallocene-catalyzed elastomers and plastomers, copolymers of isobutylene and p-alkylstyrene, halogenated copolymers of isobutylene and p-alkylstyrene, copolymers of butadiene with acrylonitrile, polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber, acrylonitrile chlorinated isoprene rubber, and combinations of two or more thereof.

The rubber compositions also preferably include a reactive cross-linking co-agent. Suitable co-agents include, but are not limited to, metal salts of unsaturated carboxylic acids having from 3 to 8 carbon atoms; unsaturated vinyl compounds and polyfunctional monomers (e.g., trimethylolpropane trimethacrylate); phenylene bismaleimide; and combinations thereof. Particular examples of suitable metal salts include, but are not limited to, one or more metal salts of acrylates, diacrylates, methacrylates, and dimethacrylates, wherein the metal is selected from magnesium, calcium, zinc, aluminum, lithium, and nickel. In a particular embodiment, the co-agent is selected from zinc salts of acrylates, diacrylates, methacrylates, and dimethacrylates. In another particular embodiment, the agent is zinc diacrylate (ZDA).

In one version, the surface hardness of the outer core layer (polyamide composition) is greater than the center hardness of the inner core (rubber composition). Preferably, the inner core has a center hardness (CH) within a range having a lower limit of 15 or 25 or 30 or 35 or 40 or 45 or 50 or 55 Shore D and an upper limit of 60 or 65 or 70 or 75 or 80 or 85 or 90 Shore D. The inner core (center) also preferably has a surface hardness (ICSH) within a range having a lower limit of 15 or 20 or 30 or 35 or 40 or 45 or 50 or 55 Shore D and an upper limit of 60 or 65 or 70 or 75 or 80 or 85 or 90 Shore D. Meanwhile, the outer core layer preferably has a surface hardness (OCLSH) within a range having a lower limit of 40 or 45 or 50 or 55 Shore D and an upper limit of 60 or 65 or 70 or 75 or 80 or 85 or 90 Shore D. In an alternative version, the polyamide composition is used to form the inner core, while the rubber composition is used to form the outer core; and preferably the center hardness of the inner core (polyamide) is greater than the surface hardness of the outer core layer (rubber).

Particularly, in one preferred instance, the center hardness of the inner core is in the range of about 30 to about 82 Shore D units and the surface hardness of the outer core is in the range of about 40 to about 87 Shore D units. More particularly, the center hardness of the inner core is about 15 Shore D units or greater and the surface hardness of the outer core is about 50 Shore D units or greater. In these instances, the surface hardness (outer core) is preferably at least 5 Shore D units greater than the center hardness (inner core).

As discussed above, in another instance, the center hardness of the inner core is greater than the surface hardness of the outer core layer. For example, the center hardness may be about 40 Shore D units or greater and the surface hardness of the outer core may be about 30 Shore D units or greater. In these instances, the center hardness (inner core) is preferably at least 5 Shore D units greater than the surface hardness (outer core).

In one preferred golf ball, the inner core (center) has a “positive” hardness gradient (that is, the outer surface of the inner core is harder than its geometric center) and the outer core layer has a “positive” hardness gradient (that is, the outer surface of the outer core layer is harder than the inner surface of the outer core layer.) In cases where both the inner core and outer core layer have “positive” hardness gradients, the outer surface hardness of the outer core layer is still preferably greater than the material hardness of the inner core (center).

In another version, the inner core (center) has a positive hardness gradient, while the outer core layer has a “negative” hardness gradient (that is, the outer surface of the outer core layer is softer than the inner surface of the outer core layer.) In yet another version, the outer core layer may have a “zero” hardness gradient. (That is, the hardness values of the outer surface of the outer core layer and the inner surface of the outer core layer are substantially the same.) Particularly, the term, “zero hardness gradient” as used herein, means a surface to center (or second surface) Shore C hardness gradient of less than 8, preferably less than 5 and most preferably less than 3 and may have a value of zero or negative 1 to negative 25. The term, “negative hardness gradient” as used herein, means a surface to center (or second surface) Shore C hardness gradient of less than zero. The terms, “zero hardness gradient” and “negative hardness gradient,” may be used herein interchangeably to refer to hardness gradients of negative 1 to negative 25. The term, “positive hardness gradient” as used herein, means a surface to center (or second surface) Shore C hardness gradient of 8 or greater, preferably 10 or greater, and most preferably 20 or greater. By the term, “steep positive hardness gradient” as used herein, it is meant surface to center (or second surface) Shore C hardness gradient of 20 or greater, more preferably 25 or greater, and most preferably 30 or greater. For example, the core may have a steep positive hardness gradient of 35, 40, or 45 Shore C or greater.

In one particular version, the hardness gradient from the geometric center of the inner core to the surface of the outer core layer is a positive hardness gradient. That is, the outer surface of the outer core layer is harder than the center of the inner core. Methods for measuring the hardness of the core and cover layers and determining the hardness gradients are discussed in further detail below.

As discussed above, the dual-core constitutes an inner core (center) and an outer core layer. The inner core preferably has a diameter within a range having a lower limit of 0.125 or 0.130 or 0.140 or 0.150 or 0.20 or 0.40 or 0.80 inches and an upper limit of 1.125 or 1.20 or 1.40 or 1.50 or 1.55 inches. More preferably, the inner core has a diameter in the range of about 0.125 to about 1.50 inches. The outer core preferably has a thickness within a range having a lower limit of 0.010 or 0.020 or 0.025 or 0.030 or 0.035 or 0.040 inches and an upper limit of 0.070 or 0.080 or 0.090 or 0.100 or 0.120 or 0.140 or 0.300 or 0.400 or 0.500 or 0.600 or 0.700 inches. Particularly, the outer core layer may have a thickness in the range of about 0.010 to about 0.570 inches and more preferably in the range of about 0.020 to about 0.280 inches. In other embodiments, particularly when the polyamide composition is used to form the inner core, the inner core may be smaller. For example, the inner core may have a diameter in the range of about 0.050 to about 1.40 inches, more preferably about 0.100 to about 0.700 inches. In such cases, the outer core layer may have a thickness in the range of about 0.020 to about 0.650 inches. The outer core layer encloses the inner core such that the two-layered core has an overall diameter within a range having a lower limit of 1.20 or 1.30 or 1.40 or 1.50 or 1.51 or 1.52 or 1.525 inches and an upper limit of 1.54 or 1.55 or 1.555 or 1.56 or 1.59 or 1.62 or 1.64 inches.

Cover Structure

The golf ball cores of this invention may be enclosed with one or more cover layers. In addition, as discussed above, an intermediate layer may be disposed between the core and cover layers. The intermediate layer preferably has good moisture vapor barrier properties to prevent moisture from penetrating into the core structure. The cover layers preferably have good impact durability and scuff-resistance. The polyamide compositions of this invention may be used to form at least one of the intermediate and/or cover layers. In other versions, the intermediate layer and cover layers are formed from other polymeric materials.

For example, the intermediate and cover layers may be formed from a wide variety of materials including, for example, polyurethanes; polyureas; copolymers, blends and hybrids of polyurethane and polyurea; ethylene acid copolymer ionomer resins (for example, Surlyn® ionomer resins and HPF® 1000 and HPF® 2000, commercially available from DuPont; Iotek® ionomers, commercially available from ExxonMobil Chemical Company; Amplify® IO ionomers of ethylene acrylic acid copolymers, commercially available from The Dow Chemical Company; and Clarix® ionomer resins, commercially available from A. Schulman Inc.); polyethylene, including, for example, low density polyethylene, linear low density polyethylene, and high density polyethylene; polypropylene; rubber-toughened olefin polymers; acid copolymers, for example, poly(meth)acrylic acid, which do not become part of an ionomeric copolymer; plastomers; flexomers; styrene/butadiene/styrene block copolymers; styrene/ethylene-butylene/styrene block copolymers; dynamically vulcanized elastomers; copolymers of ethylene and vinyl acetates; copolymers of ethylene and methyl acrylates; polyvinyl chloride resins; polyamides, poly(amide-ester) elastomers, and graft copolymers of ionomer and polyamide including, for example, Pebax® thermoplastic polyether block amides, commercially available from Arkema Inc; cross-linked trans-polyisoprene and blends thereof; polyester-based thermoplastic elastomers, such as Hytrel®, commercially available from DuPont; polyurethane-based thermoplastic elastomers, such as Elastollan®, commercially available from BASF; synthetic or natural vulcanized rubber; and combinations thereof. Castable polyurethanes, polyureas, and hybrids of polyurethanes-polyureas are particularly desirable because these materials can be used to help make a golf ball having high resiliency and a soft feel. By the term, “hybrids of polyurethane and polyurea,” it is meant to include copolymers and blends of polyurethanes and polyureas.

Polyurethanes, polyureas, and blends, copolymers, and hybrids of polyurethane/polyurea are also particularly suitable for forming cover layers. When used as cover layer materials, polyurethanes and polyureas can be thermoset or thermoplastic. Thermoset materials can be formed into golf ball layers by conventional casting or reaction injection molding techniques. Thermoplastic materials can be formed into golf ball layers by conventional compression or injection molding techniques.

In one preferred embodiment, the ball includes a dual-cover comprising inner and outer cover layers. The inner cover layer is preferably formed from a composition comprising an ionomer or a blend of two or more ionomers that helps impart hardness to the ball. The inner cover layer preferably has a material hardness of 95 Shore C or less, or less than 95 Shore C, or 92 Shore C or less, or 90 Shore C or less, or a material hardness within a range having a lower limit of 60 or 65 or 70 or 75 or 80 or 84 or 85 Shore C and an upper limit of 90 or 92 or 95 Shore C. The thickness of the inner cover layer is preferably within a range having a lower limit of 0.010 or 0.015 or 0.020 or 0.030 inches and an upper limit of 0.035 or 0.045 or 0.080 or 0.120 inches. The outer cover layer preferably has a material hardness of 85 Shore C or less. The thickness of the outer cover layer is preferably within a range having a lower limit of 0.010 or 0.015 or 0.025 inches and an upper limit of 0.035 or 0.040 or 0.055 or 0.080 inches.

In a particular embodiment, the inner cover layer is formed from a composition comprising a high acid ionomer. A particularly suitable high acid ionomer is Surlyn 8150® (DuPont). Surlyn 8150® is a copolymer of ethylene and methacrylic acid, having an acid content of 19 wt %, which is 45% neutralized with sodium. In another particular embodiment, the inner cover layer is formed from a composition comprising a high acid ionomer and a maleic anhydride-grafted non-ionomeric polymer. A particularly suitable maleic anhydride-grafted polymer is Fusabond 525D® (DuPont), which is a maleic anhydride-grafted, metallocene-catalyzed ethylene-butene copolymer having about 0.9 wt % maleic anhydride grafted onto the copolymer. One example of a blend of high acid ionomer and maleic anhydride-grafted polymer is 84 wt. %/16 wt. % blend of Surlyn 8150® and Fusabond 525D®. Blends of high acid ionomers with maleic anhydride-grafted polymers are further disclosed, for example, in U.S. Pat. Nos. 6,992,135 and 6,677,401, the entire disclosures of which are hereby incorporated herein by reference.

In another embodiment, the inner cover layer is formed from a composition comprising a 50/45/5 blend of Surlyn® 8940/Surlyn® 9650/Nucrel® 960, and, in a particularly preferred embodiment, has a material hardness of from 80 to 85 Shore C. In another particular embodiment, the inner cover layer is formed from a composition comprising a 50/25/25 blend of Surlyn® 8940/Surlyn® 9650/Surlyn® 9910, preferably having a material hardness of about 90 Shore C. In one preferred version, a blend of 50% Surlyn® 7940 and 50% Surlyn® 8940 is used to form the inner cover. In yet another particular embodiment, the inner cover layer is preferably formed from a composition comprising a 50/50 blend of Surlyn® 8940/Surlyn® 9650, preferably having a material hardness of about 86 Shore C. Surlyn® 8940 is an ethylene/methacrylic acid copolymer in which the MAA acid groups have been partially neutralized with sodium ions. Surlyn® 9650 and Surlyn® 9910 are two different grades of ethylene/methacrylic acid copolymer in which the MAA acid groups have been partially neutralized with zinc ions. Surlyn® 7940 is a copolymer of about 85% ethylene and 15% methacrylic acid that has been neutralized with lithium ions. Nucrel® 960 is an ethylene/methacrylic acid copolymer resin nominally made with 15 wt % methacrylic acid, and available from DuPont.

As discussed above, the dual-core of the golf ball may be enclosed with a single-layered or multi-layered covers. In one embodiment, a single-layered cover having a thickness in the range of about 0.015 to about 0.090 inches, more preferably about 0.030 to about 0.070 inches, is formed. The cover has a hardness of about Shore D 80 or less, more preferably 70 or less, and most preferably about 60 or less. In another embodiment, a multi-layered cover comprising inner and outer cover layers is formed, where the inner cover layer preferably has a thickness of about 0.011 inches to about 0.110 inches, more preferably about 0.02 inches to about 0.08 inches. In this version, the inner cover layer is formed from a blend of partially- or fully-neutralized ionomers, and the cover has a Shore D hardness of greater than about 55, more preferably greater than about 60, and most preferably greater than about 65. The outer cover layer, in this embodiment, preferably has a thickness of about 0.010 inches to about 0.100 inches, more preferably about 0.02 inches to about 0.06 inches, and most preferably about 0.025 inches to about 0.045 inches, with a hardness of about Shore D 80 or less, more preferably 70 or less, and most preferably about 60 or less. Thus, the cover may comprise two or more layers and preferably has an overall thickness of about 0.020 to about 0.160 inches. The inner cover layer is harder than the outer cover layer in this version. A preferred outer cover layer is a castable or reaction injection molded polyurethane, polyurea or copolymer, blend, or hybrid thereof having a Shore D hardness of about 40 to about 50. In another multi-layer cover, dual-core embodiment, the outer cover and inner cover layer materials and thickness are the same but, the hardness range is reversed; that is, the outer cover layer is harder than the inner cover layer.

Golf Ball Constructions

As discussed above, the thermoplastic polyamide compositions of this invention may be used to form a core for any suitable ball construction, including, for example, two-piece, three-piece, four-piece, and five-piece designs.

The solid cores for the golf balls of this invention may be made using any suitable conventional technique such as, for example, compression or injection molding. Typically, the inner core is formed by compression molding a slug of uncured or lightly cured rubber material into a spherical structure. The outer core, which surrounds the inner core, is formed by molding the polyamide composition over the inner core. Compression or injection molding techniques may be used. Then, the intermediate and/or cover layers are applied. Prior to this step, the core structure may be surface-treated to increase the adhesion between its outer surface and the next layer that will be applied over the core. Such surface-treatment may include mechanically or chemically-abrading the outer surface of the core. For example, the core may be subjected to corona-discharge, plasma-treatment, silane-dipping, or other treatment methods known to those in the art.

The cover layers are formed over the core or ball subassembly (the core structure and any intermediate layers disposed about the core) using a suitable technique such as, for example, compression-molding, flip-molding, injection-molding, retractable pin injection-molding, reaction injection-molding (RIM), liquid injection-molding, casting, spraying, powder-coating, vacuum-forming, flow-coating, dipping, spin-coating, and the like. Preferably, each cover layer is separately formed over the ball subassembly. For example, an ethylene acid copolymer ionomer composition may be injection-molded to produce half-shells. Alternatively, the ionomer composition can be placed into a compression mold and molded under sufficient pressure, temperature, and time to produce the hemispherical shells. The smooth-surfaced hemispherical shells are then placed around the ball subassembly in a compression mold. Under sufficient heating and pressure, the shells fuse together to form an inner cover layer that surrounds the subassembly. In another method, the ionomer composition is injection-molded directly onto the core using retractable pin injection molding. An outer cover layer comprising a polyurethane composition may be formed by using a casting process.

For example, in one version of the casting process, a liquid mixture of reactive polyurethane prepolymer and chain-extender (curing agent) is poured lower and upper mold cavities. Then, the golf ball subassembly is lowered at a controlled speed into the reactive mixture. Ball suction cups can hold the ball subassembly in place via reduced pressure or partial vacuum. After sufficient gelling of the reactive mixture (typically about 4 to about 12 seconds), the vacuum is removed and the intermediate ball is released into the mold cavity. Then, the upper mold cavity is mated with the lower mold cavity under sufficient pressure and heat. An exothermic reaction occurs when the polyurethane prepolymer and chain extender are mixed and this continues until the cover material encapsulates and solidifies around the ball subassembly. Finally, the molded balls are cooled in the mold and removed when the molded cover is hard enough so that it can be handled without deformation.

After the golf balls have been removed from the mold, they may be subjected to finishing steps such as flash-trimming, surface-treatment, marking, coating, and the like using techniques known in the art. For example, in traditional white-colored golf balls, the white-pigmented cover may be surface-treated using a suitable method such as, for example, corona, plasma, or ultraviolet (UV) light-treatment. Then, indicia such as trademarks, symbols, logos, letters, and the like may be printed on the ball's cover using pad-printing, ink-jet printing, dye-sublimation, or other suitable printing methods. Clear surface coatings (for example, primer and top-coats), which may contain a fluorescent whitening agent, are applied to the cover. The resulting golf ball has a glossy and durable surface finish.

In another finishing process, the golf balls are painted with one or more paint coatings. For example, white primer paint may be applied first to the surface of the ball and then a white top-coat of paint may be applied over the primer. Of course, the golf ball may be painted with other colors, for example, red, blue, orange, and yellow. As noted above, markings such as trademarks and logos may be applied to the painted cover of the golf ball. Finally, a clear surface coating may be applied to the cover to provide a shiny appearance and protect any logos and other markings printed on the ball.

Referring to FIG. 1, one version of a golf ball that can be made in accordance with this invention is generally indicated at (8). The ball (8) contains a dual-core (10) having an inner core (center) (10 a) and outer core layer (10 b) surrounded by a single-layered cover (12). The center (10 a) is formed preferably from a rubber composition as discussed above. The outer core layer (10 b) is formed from a polyamide composition as discussed above. In FIG. 2, a golf ball (15) containing the above-described dual-core (10) is surrounded by a dual-cover (18) having an inner cover layer (18 a) and outer cover layer (18 b), which may be formed from any of the cover materials described above.

The surfaces of the golf balls shown in FIGS. 1-2 may have various dimple patterns to modify the aerodynamic properties of the ball. It should be understood the golf balls shown in FIGS. 1-2 are for illustrative purposes only and not meant to be restrictive. Other golf ball constructions can be made in accordance with this invention.

For example, golf balls having an inner core and outer core may be prepared, wherein the polyamide-based composition of this invention is used to form the inner core; and a rubber or other suitable composition may be used to form the outer-core. In one preferred embodiment, the surface hardness of the outer core layer (polyamide-based) is less than the center hardness of the inner core (rubber-based). In another example, the polyamide-based composition is used to form both the inner core and outer core layers.

In yet another example, a golf ball containing an inner core (center); an intermediate core layer; and an outer core layer may be made. The center preferably has a diameter within a range having a lower limit of 0.100 or 0.125 or 0.250 inches and an upper limit of 0.375 or 0.500 or 0.750 or 1.00 or 1.30 inches. The intermediate core layer preferably has a thickness within a range having a lower limit of 0.050 or 0.100 or 0.150 or 0.200 inches and an upper limit of 0.300 or 0.350 or 0.400 or 0.500 inches. The outer core layer encloses the center and intermediate core layer structure such that the multi-layer core has an overall diameter within a range having a lower limit of 1.40 or 1.45 or 1.50 or 1.55 inches and an upper limit of 1.58 or 1.60 or 1.62 or 1.66 inches.

In one embodiment, the inner core (center) is made of the polyamide-based composition of this invention. The surrounding intermediate core layer is made of a rubber composition comprising a base rubber such as, for example, polybutadiene, polyisoprene, ethylene propylene rubber (EPR), ethylene propylene diene rubber (EPDM), styrene-butadiene rubber, styrenic block copolymer rubbers (such as “SI”, “SIS”, “SB”, “SBS”, “SIBS”, and the like, where “S” is styrene, “I” is isobutylene, and “B” is butadiene), polyalkenamers such as, for example, polyoctenamer, butyl rubber, halobutyl rubber, and polystyrene elastomers. Finally, the outer core layer also is made of the polyamide-based composition of this invention.

In one preferred embodiment, the center and outer core layers (polyamide compositions) preferably each has an outer surface hardness of 40 Shore D or greater, more preferably a surface hardness of 60 Shore C or greater, and most preferably a surface hardness of 70 Shore C or greater. For example, the center may have an outer surface hardness within a range having a lower limit of 45 or 55 or 65 Shore D and an upper limit of 75 or 85 or 95 Shore D. Meanwhile, the intermediate core layer (rubber composition) may have an outer surface hardness that is less than that of the center and is preferably 50 Shore C or less; or 60 Shore C or less; or 70 Shore C or less; or 75 Shore C or less; or 80 Shore C or less.

As discussed above, the golf ball cores of this invention may be enclosed with one or more cover layers. For example, a golf ball having inner and outer cover layers may be made. In another version, a three-layered cover comprising inner, intermediate, and outer cover layers may be made. The multi-layered cover of the golf balls of this invention provide the ball with a variety of advantageous mechanical and playing performance properties as discussed further below. In general, the hardness and thickness of the different cover layers may vary depending upon the desired ball construction. In addition, as discussed above, an intermediate layer may be disposed between the core and cover layers. The cover layers preferably have good impact durability, toughness, and wear-resistance. The polyamide-based compositions of this invention may be used to form at least one of the cover layers.

In one version, the golf ball includes a multi-layered cover comprising inner and outer cover layers. The inner cover layer may be formed from a composition comprising an ionomer or a blend of two or more ionomers that helps impart hardness to the ball. The outer cover is preferably formed of the polyamide-based composition of this invention as described above.

In another version, the inner cover layer is formed from the polyamide-based composition of this invention, and the outer cover layer is formed from a suitable thermoset or thermoplastic composition. In one particularly preferred version, a two-layered cover is made. For example, a cover assembly having inner and outer cover layers, wherein a relatively hard cover is disposed about a relatively soft cover may be made. Alternatively, a relatively soft cover may be disposed about a relatively hard cover. The polyamide-based compositions of this invention may be used to form at least one of the cover layers. Other thermoplastic or thermoset compositions as described above may be used to form the other cover layer in the two-layered cover assembly.

In another particularly preferred version, a three-layered cover is made. For example, a cover assembly having inner and outer cover layers, wherein an intermediate cover layer is disposed between the inner and outer cover layers. In such a construction, the polyamide-based compositions of this invention may be used to form at least one of the inner, intermediate, or outer cover layers.

It is recognized that additional golf ball constructions can be made without departing from the spirit and scope of the present invention. For example, in another version, a golf ball containing a multi-layered core having: i) an inner core (center) made of a rubber composition as described above; ii) a surrounding intermediate core layer made of the polyamide composition of this invention; and iii) an outer core layer made of a rubber composition, can be manufactured. In yet another version, both the inner core (center) and intermediate core layer each are made of a rubber composition; and the outer core layer is made of the polyamide composition of this invention. In a further embodiment, both the inner core (center) and intermediate core layer are made of the polyamide composition of this invention; and the outer core layer is made of a rubber composition.

Test Methods

Hardness.

The center hardness of a core is obtained according to the following procedure. The core is gently pressed into a hemispherical holder having an internal diameter approximately slightly smaller than the diameter of the core, such that the core is held in place in the hemispherical portion of the holder while concurrently leaving the geometric central plane of the core exposed. The core is secured in the holder by friction, such that it will not move during the cutting and grinding steps, but the friction is not so excessive that distortion of the natural shape of the core would result. The core is secured such that the parting line of the core is roughly parallel to the top of the holder. The diameter of the core is measured 90 degrees to this orientation prior to securing. A measurement is also made from the bottom of the holder to the top of the core to provide a reference point for future calculations. A rough cut is made slightly above the exposed geometric center of the core using a band saw or other appropriate cutting tool, making sure that the core does not move in the holder during this step. The remainder of the core, still in the holder, is secured to the base plate of a surface grinding machine. The exposed ‘rough’ surface is ground to a smooth, flat surface, revealing the geometric center of the core, which can be verified by measuring the height from the bottom of the holder to the exposed surface of the core, making sure that exactly half of the original height of the core, as measured above, has been removed to within 0.004 inches. Leaving the core in the holder, the center of the core is found with a center square and carefully marked and the hardness is measured at the center mark according to ASTM D-2240. Additional hardness measurements at any distance from the center of the core can then be made by drawing a line radially outward from the center mark, and measuring the hardness at any given distance along the line, typically in 2 mm increments from the center. The hardness at a particular distance from the center should be measured along at least two, preferably four, radial arms located 180° apart, or 90° apart, respectively, and then averaged. All hardness measurements performed on a plane passing through the geometric center are performed while the core is still in the holder and without having disturbed its orientation, such that the test surface is constantly parallel to the bottom of the holder, and thus also parallel to the properly aligned foot of the durometer.

The outer surface hardness of a golf ball layer is measured on the actual outer surface of the layer and is obtained from the average of a number of measurements taken from opposing hemispheres, taking care to avoid making measurements on the parting line of the core or on surface defects, such as holes or protrusions. Hardness measurements are made pursuant to ASTM D-2240 “Indentation Hardness of Rubber and Plastic by Means of a Durometer.” Because of the curved surface, care must be taken to ensure that the golf ball or golf ball subassembly is centered under the durometer indenter before a surface hardness reading is obtained. A calibrated, digital durometer, capable of reading to 0.1 hardness units is used for the hardness measurements. The digital durometer must be attached to, and its foot made parallel to, the base of an automatic stand. The weight on the durometer and attack rate conforms to ASTM D-2240.

In certain embodiments, a point or plurality of points measured along the “positive” or “negative” gradients may be above or below a line fit through the gradient and its outermost and innermost hardness values. In an alternative preferred embodiment, the hardest point along a particular steep “positive” or “negative” gradient may be higher than the value at the innermost portion of the inner core (the geometric center) or outer core layer (the inner surface)—as long as the outermost point (i.e., the outer surface of the inner core) is greater than (for “positive”) or lower than (for “negative”) the innermost point (i.e., the geometric center of the inner core or the inner surface of the outer core layer), such that the “positive” and “negative” gradients remain intact.

As discussed above, the direction of the hardness gradient of a golf ball layer is defined by the difference in hardness measurements taken at the outer and inner surfaces of a particular layer. The center hardness of an inner core and hardness of the outer surface of an inner core in a single-core ball or outer core layer are readily determined according to the test procedures provided above. The outer surface of the inner core layer (or other optional intermediate core layers) in a dual-core ball are also readily determined according to the procedures given herein for measuring the outer surface hardness of a golf ball layer, if the measurement is made prior to surrounding the layer with an additional core layer. Once an additional core layer surrounds a layer of interest, the hardness of the inner and outer surfaces of any inner or intermediate layers can be difficult to determine. Therefore, for purposes of the present invention, when the hardness of the inner or outer surface of a core layer is needed after the inner layer has been surrounded with another core layer, the test procedure described above for measuring a point located 1 mm from an interface is used.

Also, it should be understood that there is a fundamental difference between “material hardness” and “hardness as measured directly on a golf ball.” For purposes of the present invention, material hardness is measured according to ASTM D2240 and generally involves measuring the hardness of a flat “slab” or “button” formed of the material. Surface hardness as measured directly on a golf ball (or other spherical surface) typically results in a different hardness value. The difference in “surface hardness” and “material hardness” values is due to several factors including, but not limited to, ball construction (that is, core type, number of cores and/or cover layers, and the like); ball (or sphere) diameter; and the material composition of adjacent layers. It also should be understood that the two measurement techniques are not linearly related and, therefore, one hardness value cannot easily be correlated to the other. Shore hardness (for example, Shore C or Shore D hardness) was measured according to the test method ASTM D-2240.

Compression.

As disclosed in Jeff Dalton's Compression by Any Other Name, Science and Golf IV, Proceedings of the World Scientific Congress of Golf (Eric Thain ed., Routledge, 2002) (“J. Dalton”), several different methods can be used to measure compression, including Atti compression, Riehle compression, load/deflection measurements at a variety of fixed loads and offsets, and effective modulus. For purposes of the present invention, “compression” refers to Atti compression and is measured according to a known procedure, using an Atti compression test device, wherein a piston is used to compress a ball against a spring. The travel of the piston is fixed and the deflection of the spring is measured. The measurement of the deflection of the spring does not begin with its contact with the ball; rather, there is an offset of approximately the first 1.25 mm (0.05 inches) of the spring's deflection. Very low stiffness cores will not cause the spring to deflect by more than 1.25 mm and therefore have a zero compression measurement. The Atti compression tester is designed to measure objects having a diameter of 42.7 mm (1.68 inches); thus, smaller objects, such as golf ball cores, must be shimmed to a total height of 42.7 mm to obtain an accurate reading. Conversion from Atti compression to Riehle (cores), Riehle (balls), 100 kg deflection, 130-10 kg deflection or effective modulus can be carried out according to the formulas given in J. Dalton. Compression may be measured as described in McNamara et al., U.S. Pat. No. 7,777,871, the disclosure of which is hereby incorporated by reference.

Coefficient of Restitution (“COR”).

The COR is determined according to a known procedure, wherein a golf ball or golf ball subassembly (for example, a golf ball core) is fired from an air cannon at two given velocities and a velocity of 125 ft/s is used for the calculations. Ballistic light screens are located between the air cannon and steel plate at a fixed distance to measure ball velocity. As the ball travels toward the steel plate, it activates each light screen and the ball's time period at each light screen is measured. This provides an incoming transit time period which is inversely proportional to the ball's incoming velocity. The ball makes impact with the steel plate and rebounds so it passes again through the light screens. As the rebounding ball activates each light screen, the ball's time period at each screen is measured. This provides an outgoing transit time period which is inversely proportional to the ball's outgoing velocity. The COR is then calculated as the ratio of the ball's outgoing transit time period to the ball's incoming transit time period (COR=V_(out)/V_(in)=T_(in)/T_(out)).

When numerical lower limits and numerical upper limits are set forth herein, it is contemplated that any combination of these values may be used. Other than in the operating examples, or unless otherwise expressly specified, all of the numerical ranges, amounts, values and percentages such as those for amounts of materials and others in the specification may be read as if prefaced by the word “about” even though the term “about” may not expressly appear with the value, amount or range. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention.

All patents, publications, test procedures, and other references cited herein, including priority documents, are fully incorporated by reference to the extent such disclosure is not inconsistent with this invention and for all jurisdictions in which such incorporation is permitted.

It is understood that the compositions and golf ball products described and illustrated herein represent only some embodiments of the invention. It is appreciated by those skilled in the art that various changes and additions can be made to compositions and products without departing from the spirit and scope of this invention. It is intended that all such embodiments be covered by the appended claims. 

We claim:
 1. A golf ball, comprising: a) a core comprising an inner core and outer core layer, the inner core having an outer surface and geometric center and the outer core layer having an outer surface and inner surface; the inner core comprising a rubber composition and the outer core consisting essentially of a polyamide composition, the polyamide composition consisting essentially of: i) about 40 to about 97% by weight polyamide; ii) about 1 to about 60% by weight fatty acid amide; iii) about 1 to about 60% by weight of an acid copolymer of ethylene and α,β-unsaturated carboxylic acid, optionally including a softening monomer selected from the group consisting of alkyl acrylates and methacrylates; iv) a cation source present in an amount sufficient to neutralize from about 0 to about 100% of all acid groups present in the composition; and v) about 1 to about 60% by weight of a plasticizer; wherein the plasticizer is an alkyl oleate selected from the group consisting of methyl oleate, ethyl oleate, propyl oleate, butyl oleate, and octyl oleate, and mixtures thereof; and wherein the center of the inner core and surface of the of the outer core layer each has a hardness, and the surface hardness of the outer core layer is greater than the center hardness of the inner core; and b) a cover having at least one layer disposed about the core.
 2. The golf ball of claim 1, wherein the acid copolymer is selected from the group consisting of ethylene/(meth)acrylic acid/n-butyl acrylate; ethylene/(meth)acrylic acid/ethyl; ethylene/(meth)acrylic acid/methyl acrylate; ethylene/(meth)acrylic acid/n-butyl acrylate; and ethylene/(meth)acrylic acid/isobutyl acrylate.
 3. The golf ball of claim 1, wherein the acid copolymer of ethylene and an α,β-unsaturated carboxylic acid does not include a softening monomer, and wherein the acid is selected from acrylic acid and methacrylic acid and is present in the acid copolymer in an amount of from about 15 to about 30 weight %, based on the total weight of the acid copolymer.
 4. The golf ball of claim 1, wherein the acid copolymer contains acid groups such that greater than 70% of the acid groups are neutralized.
 5. The golf ball of claim 1, wherein the plasticizer is present in the composition in an amount of about 3 to about 30% by weight.
 6. The golf ball of claim 1, wherein the center hardness of the inner core is about 15 Shore D or greater and the surface hardness of the outer core is about 20 Shore D or greater, the surface hardness of the outer core layer being greater than the center hardness of the inner core.
 7. The golf ball of claim 1, wherein the cover is a single layer having a thickness of about 0.015 to about 0.090 inches and is formed from a thermoplastic or thermoset material.
 8. The golf ball of claim 1, wherein the cover comprises two or more layers and has an overall thickness of about 0.020 to about 0.160 inches and wherein each cover layer is formed from a thermoplastic or thermoset material.
 9. A golf ball, comprising: a) a core comprising an inner core and outer core layer, the inner core having an outer surface and geometric center and the outer core layer having an outer surface and inner surface; the inner core comprising a rubber composition and the outer core consisting essentially of a polyamide composition, the polyamide composition consisting essentially of: i) about 40 to about 97% by weight polyamide; ii) about 1 to about 60% by weight fatty acid amide; iii) about 1 to about 60% by weight of an acid copolymer of ethylene and α,β-unsaturated carboxylic acid, optionally including a softening monomer selected from the group consisting of alkyl acrylates and methacrylates; iv) a cation source present in an amount sufficient to neutralize from about 0 to about 100% of all acid groups present in the composition; and v) about 1 to about 60% by weight of a plasticizer; wherein the plasticizer is selected from the group consisting of benzoate esters and carbonate esters, and wherein the center of the inner core and surface of the of the outer core layer each has a hardness, and the surface hardness of the outer core layer is greater than the center hardness of the inner core; and b) a cover having at least one layer disposed about the core.
 10. The golf ball of claim 9, wherein the plasticizer is selected from the group consisting of dipropylene glycol dibenzoate and propylene carbonate. 